docs: explain using symlinks for the usual command names

[ddy314]

Describe the changes done on this pull request

Document using /usr/local/bin symlinks when a distribution packages sudo-rs with suffixed command names. Explain PATH ordering, absolute-path invocations, existing aliases, and how to undo the setup; prefer the distribution's selection mechanism when one is available.

Fixes #1478, following the maintainer's suggestion to document system-wide symlinks.

Validated the example in temporary directories with dummy executables: PATH lookup selects the linked executable, absolute paths still select the original, ln -s refuses an existing destination, and removing the links restores the original PATH lookup. No system installation was changed. git diff --check passes; Rust checks are not applicable to this README-only change.

Pull Request Checklist

• I have read and accepted the code of conduct for this project.
• I have tested, formatted and ran clippy over my changes. (Documentation-only validation described above.)
• I have commented and documented my changes.
• This pull request will fix an issue where a proper discussion about a solution has taken place: Recommend to set as symlink rather than alias #1478.