Add CONTRIBUTING.md file


Point potential contributors to contribute.qt-project.org.

Change-Id: Ie396502f0aa3890a0daf60941d995ad5d43f59e2
Reviewed-by: Paul Wicking <paul.wicking@qt.io>
commitf4815a51ef3d5756fc41eb2845c1ae48de8a3ddc
parentb72bef8c67c36aa6858c066612be254872e9f459
authorKai Köhne <kai.koehne@qt.io>
committerKai Köhne <kai.koehne@qt.io>
commit timeWed, 22 Apr 2026 07:16:01 +0000