* Replace information CONTRIBUTING.md because it is redundantly stored
in each project repository. Instead, CONTRIBUTING.md now links to the
project website that centralizes the information.
* Links to kuksa-dev mailing list and Zoom meeting added.
* References to Bugzilla have been removed because GitHub issues are
used instead.
* Clean code is mentioned to encourage a good code style and be able to
refer to it when reviewing pull requests.
* The documentation section has been updated to what has been agreed on
lately.
* Practical hints for commit style have been added.

Signed-off-by: Sebastian Lohmeier <Sebastian.Lohmeier@bosch-si.com>