docs: sync FLAGS.md with actual CLI arguments

[SpiliosDimakopoulos]

docs/FLAGS.md was out of sync with the actual argparse definitions in
main.py:

• Removed -p, --permute: this flag doesn't exist anywhere in the
  codebase (verified via repo-wide grep). Pattern-based permutations are
  generated inline via -u/-e (e.g. -u "john[a-c]"), as already shown
  correctly elsewhere in this same file and in the README.
• Added -U, --update and --version: both exist in main.py's
  argparse but were missing from this table.

Docs only, no code changes.

[VamatoHD]

Removed -p, --permute: this flag doesn't exist anywhere in the
codebase (verified via repo-wide grep). Pattern-based permutations are
generated inline via -u/-e (e.g. -u "john[a-c]"), as already shown
correctly elsewhere in this same file and in the README.

Even though you stated this, this change wasn't implemented in this PR.

[kaifcodec]

@VamatoHD Seems like the PR author is not going to respond on these also there are open questions and change requested in #452 as well 2 days ago.
I will convert these PRs to draft if I don't recieve any response.

[kaifcodec]

This PR will be covered in #459 .
Closing it.