docs: update pre-commit exclude and force-exclude explanation

[Nidhijha-10]

This PR improves the documentation for how Black handles exclude patterns when
used with pre-commit. Since pre-commit passes file paths directly to Black,
Black's normal exclude rules do not apply unless --force-exclude is used.

The updated section explains:

• why pre-commit's own exclude should be preferred,

• how exclusions can be configured in pyproject.toml,

• when --force-exclude is helpful as a fallback.

  Closes Document using pre-commit and how --force-exclude can help  #3015