docs: limit pre-commit hook to requirements files

[gcomneno]

Closes #334.

Updates the README pre-commit example to include a files filter so the pip-audit hook only runs when requirements files change.

[gcomneno]

Note: I kept the regex intentionally simple for readability. If you’d prefer broader matching (e.g. or ), I can adjust it.

[gcomneno]

Note: I kept the files regex intentionally simple for readability. If you’d prefer broader matching (e.g. requirements/.txt or requirements-.txt), I can adjust it.