add admin notes for crowdin administration (#19255)
### Summary of the issue:
This pull request adds new documentation to help Crowdin administrators
manage translations for NVDA. The main focus is on providing clear
instructions for adding languages, translation files, and translators.
Added a new section in `projectDocs/translating/admin.md` with
step-by-step instructions for adding new languages via Crowdin settings
and integrating them into NVDA.
