This commit contains several changes. It completely overhauls the README, switching the context
from a generic GitLab-project to a specific 'QUIQQER Apple authentication and registration' module.
Features, installation instructions, contribution guidelines and support details were added to
improve user understanding.

In terms of code modifications:
- Updated `getClientId.php` to fetch Apple's API Client-ID instead of Google's.
- Removed `google/apiclient` from `composer.json` dependencies.
- Updated function 'getClientId' in `Apple.php` to call 'quiqqer/authapple' instead of
'quiqqer/authgoogle'.
- Changed comments in `Auth.php` to reflect that it handles Apple authentication instead of
Google's.

These fixes help ensure code coherence according to the Apple authentication module.