extend documentation/tutorial for `localization-tool`

[moritz-gross]

There should be an explanation of how the .yaml files for the rules work, basically an extended version of
what you explained in the DAISY meeting.
I added some info to PythonScripts/audit_translations/README.md when I first started working on it,
but it is definitely incomplete.

Additionally extend the info shown in uv run audit-translations --help, or maybe add a reference to the README.md file so that it's not redundant.