[TASK] Use current git repository links

README.md and CONTRIBUTING.md use the current repository links with this change.
The change also includes several minor edits.

Resolves: #98260
Releases: main, 11.5, 10.4
Change-Id: I77d4741df4134ae0babec2415cd8f5345592e29e
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/75634


Tested-by: core-ci <typo3@b13.com>
Tested-by: Oliver Bartsch <bo@cedev.de>
Reviewed-by: Stephan Großberndt <stephan.grossberndt@typo3.org>
Reviewed-by: Oliver Bartsch <bo@cedev.de>