[TASK] README.md Contribution Workflow Link

Link to docs.typo3.org instead of wiki.

Change-Id: Ib76f1fb11b9cc0e8069407528ab058f7ae2e984e
Resolves: #78510
Releases: master
Reviewed-on: https://review.typo3.org/50448


Reviewed-by: Mathias Brodala <mbrodala@pagemachine.de>
Reviewed-by: Joerg Boesche <typo3@joergboesche.de>
Tested-by: TYPO3com <no-reply@typo3.com>
Tested-by: Joerg Boesche <typo3@joergboesche.de>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Tested-by: Wouter Wolters <typo3@wouterwolters.nl>