[tongwentao]

Add a FAQ explaining why a directory-only gitignore pattern matches build/ but not the bare path build when using match_file() or match_files().

The distinction discussed in #89 is easy to miss: these methods match supplied paths without checking the filesystem, and pathlib.Path does not preserve a trailing slash. Include executable examples and point readers to the entry-based methods, which supply directory markers automatically. Matching behavior is unchanged.

Behavior and review notes

The examples distinguish matching a path string from discovering filesystem metadata. Creating a real directory named build does not make a bare build string acquire a directory marker in match_file(). Readers who already have filesystem entries are directed to the entry-based API instead of being advised to alter matching rules or assume Path preserves a trailing separator.

Validation on Linux, Python 3.13.5:

• All five statements in the new FAQ passed with doctest.
• The project's python -m unittest discover -t . -s tests/ command completed successfully. Optional RE2/Hyperscan cases were skipped because those extras are not installed.
• The configured strict Sphinx command (sphinx-build -aWEnqb html) passed; checked the rendered FAQ and navigation.
• git diff --check passed.

Related to #89; this documents the existing behavior rather than changing or closing that issue. Prepared and validated with Codex assistance.