doc: Merge release notes fragments

- Merge release notes fragments into release-notes.md

- Remove downgrading notes (as I understand this pertains to `<0.15`,
  this doesn't warrant mentioning anymore)

Tree-SHA512: 839e30807651ff53efa713f707ba0744c6c6c9bcb2c9c8afc0e299c93f772cc9a0ef294ba7e15f7049280556404d9b2e96b74f28e456aa36130af05bc7cfe035

7 files changed, 56 insertions, 60 deletions

diff --git a/doc/release-notes-14021.md b/doc/release-notes-14021.md
deleted file mode 100644
index 4797a95bdb..0000000000
--- a/doc/release-notes-14021.md
+++ /dev/null
@@ -1,11 +0,0 @@
-Miscellaneous RPC Changes
--------------------------
-- Descriptors with key origin information imported through `importmulti` will have their key origin information stored in the wallet for use with creating PSBTs.
-- If `bip32derivs` of both `walletprocesspsbt` and `walletcreatefundedpsbt` is set to true but the key metadata for a public key has not been updated yet, then that key will have a derivation path as if it were just an independent key (i.e. no derivation path and its master fingerprint is itself)
-
-Miscellaneous Wallet changes
-----------------------------
-
-- The key metadata will need to be upgraded the first time that the HD seed is available.
-For unencrypted wallets this will occur on wallet loading.
-For encrypted wallets this will occur the first time the wallet is unlocked.
diff --git a/doc/release-notes-14481.md b/doc/release-notes-14481.md
deleted file mode 100644
index ea8fc3c34e..0000000000
--- a/doc/release-notes-14481.md
+++ /dev/null
@@ -1,9 +0,0 @@
-Low-level RPC changes
-----------------------
-
-The `listunspent` RPC has been modified so that it also returns `witnessScript`,
-the witness script in the case of a P2WSH or P2SH-P2WSH output.
-
-The `signrawtransactionwithkey` and `signrawtransactionwithwallet` RPCs have been
-modified so that they also optionally accept a `witnessScript`, the witness script in the
-case of a P2WSH or P2SH-P2WSH output. This is compatible with the change to `listunspent`.
diff --git a/doc/release-notes-14491.md b/doc/release-notes-14491.md
deleted file mode 100644
index 1cf36e85cf..0000000000
--- a/doc/release-notes-14491.md
+++ /dev/null
@@ -1,5 +0,0 @@
-Descriptor import support
----------------------
-
-The `importmulti` RPC now supports importing of addresses from descriptors. A "desc" parameter can be provided instead of the "scriptPubKey" in a request, as well as an optional range for ranged descriptors to specify the start and end of the range to import. More information about
-descriptors can be found [here](https://github.com/bitcoin/bitcoin/blob/master/doc/descriptors.md).
diff --git a/doc/release-notes-14667.md b/doc/release-notes-14667.md
deleted file mode 100644
index 5cb1d0aee7..0000000000
--- a/doc/release-notes-14667.md
+++ /dev/null
@@ -1,4 +0,0 @@
-New RPC methods
-------------
-
-- `deriveaddresses` returns one or more addresses corresponding to an [output descriptor](/doc/descriptors.md).
diff --git a/doc/release-notes-15226.md b/doc/release-notes-15226.md
deleted file mode 100644
index 3be84db3e9..0000000000
--- a/doc/release-notes-15226.md
+++ /dev/null
@@ -1,8 +0,0 @@
-Miscellaneous RPC changes
-------------
-
-- The RPC `createwallet` now has an optional `blank` argument that can be used to create a blank wallet.
-Blank wallets do not have any keys or HD seed.
-They cannot be opened in software older than 0.18.
-Once a blank wallet has a HD seed set (by using `sethdseed`) or private keys, scripts, addresses, and other watch only things have been imported, the wallet is no longer blank and can be opened in 0.17.x.
-Encrypting a blank wallet will also set a HD seed for it.
diff --git a/doc/release-notes-15393.md b/doc/release-notes-15393.md
deleted file mode 100644
index f478dc798d..0000000000
--- a/doc/release-notes-15393.md
+++ /dev/null
@@ -1,4 +0,0 @@
-Dependencies
-------------
-
-- The minimum required version of QT has been increased from 5.2 to 5.5.1 (the [depends system](https://github.com/bitcoin/bitcoin/blob/master/depends/README.md) provides 5.9.7)
diff --git a/doc/release-notes.md b/doc/release-notes.md
index a6408cf1e6..16146288da 100644
--- a/doc/release-notes.md
+++ b/doc/release-notes.md
@@ -24,39 +24,28 @@ shut down (which might take a few minutes for older versions), then run the
 installer (on Windows) or just copy over `/Applications/Bitcoin-Qt` (on Mac)
 or `bitcoind`/`bitcoin-qt` (on Linux).
 
-The first time you run version 0.15.0, your chainstate database will be converted to a
-new format, which will take anywhere from a few minutes to half an hour,
-depending on the speed of your machine.
+The first time you run version 0.15.0 or newer, your chainstate database
+will be converted to a new format, which will take anywhere from a few minutes
+to half an hour, depending on the speed of your machine.
 
 Note that the block database format also changed in version 0.8.0 and there is no
 automatic upgrade code from before version 0.8 to version 0.15.0. Upgrading
 directly from 0.7.x and earlier without redownloading the blockchain is not supported.
 However, as usual, old wallet versions are still supported.
 
-Downgrading warning
--------------------
-
-The chainstate database for this release is not compatible with previous
-releases, so if you run 0.15 and then decide to switch back to any
-older version, you will need to run the old release with the `-reindex-chainstate`
-option to rebuild the chainstate data structures in the old format.
-
-If your node has pruning enabled, this will entail re-downloading and
-processing the entire blockchain.
-
 Compatibility
 ==============
 
 Bitcoin Core is supported and extensively tested on operating systems using
-the Linux kernel, macOS 10.10+, and Windows 7 and newer.  It is not recommended
+the Linux kernel, macOS 10.10+, and Windows 7 and newer. It is not recommended
 to use Bitcoin Core on unsupported systems.
 
 Bitcoin Core should also work on most other Unix-like systems but is not
-frequently tested on them.
+as frequently tested on them.
 
-From 0.17.0 onwards, macOS <10.10 is no longer supported.  0.17.0 is
+From 0.17.0 onwards, macOS <10.10 is no longer supported. 0.17.0 is
 built using Qt 5.9.x, which doesn't support versions of macOS older than
-10.10.  Additionally, Bitcoin Core does not yet change appearance when
+10.10. Additionally, Bitcoin Core does not yet change appearance when
 macOS "dark mode" is activated.
 
 In addition to previously-supported CPU platforms, this release's
@@ -207,6 +196,9 @@ New RPCs
   moment, it returns an array of the currently active commands and how
   long they've been running.
 
+- `deriveaddresses` returns one or more addresses corresponding to an
+  [output descriptor](/doc/descriptors.md).
+
 Updated RPCs
 ------------
 
@@ -275,6 +267,23 @@ in the Low-level Changes section below.
 - The `unloadwallet` RPC is now synchronous, meaning it will not return
   until the wallet is fully unloaded.
 
+- The `importmulti` RPC now supports importing of addresses from descriptors. A
+  "desc" parameter can be provided instead of the "scriptPubKey" in a request, as
+  well as an optional range for ranged descriptors to specify the start and end
+  of the range to import. More information about descriptors can be found
+  [here](https://github.com/bitcoin/bitcoin/blob/master/doc/descriptors.md).
+
+- The `listunspent` RPC has been modified so that it also returns `witnessScript`,
+  the witness script in the case of a P2WSH or P2SH-P2WSH output.
+
+- The RPC `createwallet` now has an optional `blank` argument that can be used
+  to create a blank wallet. Blank wallets do not have any keys or HD seed.
+  They cannot be opened in software older than 0.18. Once a blank wallet has a
+  HD seed set (by using `sethdseed`) or private keys, scripts, addresses, and
+  other watch only things have been imported, the wallet is no longer blank and
+  can be opened in 0.17.x. Encrypting a blank wallet will also set a HD seed
+  for it.
+
 REST changes
 ------------
 
@@ -305,7 +314,7 @@ Graphical User Interface (GUI)
   sdk version)
 
 Tools
-----
+-----
 
 - A new `bitcoin-wallet` tool is now distributed alongside Bitcoin
   Core's other executables.  Without needing to use any RPCs, this tool
@@ -314,6 +323,14 @@ Tools
   encrypted, whether it uses an HD seed, how many transactions it
   contains, and how many address book entries it has.
 
+Dependencies
+------------
+
+- The minimum required version of QT (when building the GUI) has been increased
+  from 5.2 to 5.5.1 (the [depends
+  system](https://github.com/bitcoin/bitcoin/blob/master/depends/README.md)
+  provides 5.9.7)
+
 Low-level changes
 =================
 
@@ -330,6 +347,19 @@ RPC
 - A new `submitheader` RPC allows submitting block headers independently
   from their block.  This is likely only useful for testing.
 
+- The `signrawtransactionwithkey` and `signrawtransactionwithwallet` RPCs have been
+  modified so that they also optionally accept a `witnessScript`, the witness script in the
+  case of a P2WSH or P2SH-P2WSH output. This is compatible with the change to `listunspent`.
+
+- Descriptors with key origin information imported through `importmulti` will
+  have their key origin information stored in the wallet for use with creating
+  PSBTs.
+
+- If `bip32derivs` of both `walletprocesspsbt` and `walletcreatefundedpsbt` is
+  set to true but the key metadata for a public key has not been updated yet,
+  then that key will have a derivation path as if it were just an independent
+  key (i.e. no derivation path and its master fingerprint is itself)
+
 Configuration
 -------------
 
@@ -354,6 +384,13 @@ Network
   the `setban` RPC, all connections from that peer will still be
   rejected.
 
+Wallet
+-------
+
+- The key metadata will need to be upgraded the first time that the HD seed is
+  available.  For unencrypted wallets this will occur on wallet loading.  For
+  encrypted wallets this will occur the first time the wallet is unlocked.
+
 Security
 --------