doc: Add anchors.dat to files.md
doc: Add anchors.dat to files.md

Summary:
This is a backport of [[https://github.com/bitcoin/bitcoin/pull/17428 | core#17428]] [7/7]
https://github.com/bitcoin/bitcoin/pull/17428/commits/a490d074b3491427afbd677f5fa635b910f8bb34

Depends on D10512

Test Plan: proofreading

Reviewers: #bitcoin_abc, majcosta

Reviewed By: #bitcoin_abc, majcosta

Differential Revision: https://reviews.bitcoinabc.org/D10513

Bitcoin-ABC/bitcoin-abc,Bitcoin-ABC/bitcoin-abc,Bitcoin-ABC/bitcoin-abc,Bitcoin-ABC/bitcoin-abc,Bitcoin-ABC/bitcoin-abc,Bitcoin-ABC/bitcoin-abc,Bitcoin-ABC/bitcoin-abc,Bitcoin-ABC/bitcoin-abc,Bitcoin-ABC/bitcoin-abc,Bitcoin-ABC/bitcoin-abc,Bitcoin-ABC/bitcoin-abc,Bitcoin-ABC/bitcoin-abc,Bitcoin-ABC/bitcoin-abc