doc: Added regtest config for linearize script

Updated the example-linearize.cfg file to include support for the regtest chain network config which is used by the ./linearize-data.py

Problem:

Without the regtest magic, genesis hash and path config, the `linearize-data.py` script cannot generate a bootstrap.dat file.

Example of error:

./linearize-data.py ./linearize.cfg
Read 102 hashes
Genesis block not found in hashlist

Solution:

Added netmagic, genesis and input example parameters to file.

Resolution

1. Starting bitcoind in regtest mode
2. bitcoin-cli generatetoaddress 101 $(bitcoin-cli getnewaddress)
3. ./linearize-hashes.py ./linearize.cfg > ./hashlist.txt
4. ./linearize-data.py ./linearize.cfg

Example after fix:
$ ./linearize-data.py ./linearize.cfg
Read 102 hashes
Input file /Users/gr0kchain/.bitcoin/regtest/blocks/blk00000.dat
Output file /Users/gr0kchain/Downloads/bootstrap.dat
Done (102 blocks written)

0 files changed, 0 insertions, 0 deletions