Add CONTRIBUTING.md file


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

Change-Id: Id4dbc0dda57fe316f5d338dd0ef407b278287671
Reviewed-by: Paul Wicking <paul.wicking@qt.io>
commit5287cf1442ce2e639983d26ea79c8770ee5f9eab
parent778fa2d33cd4d7bcaaf0ce4e704de77ce5a4a683
authorKai Köhne <kai.koehne@qt.io>
committerKai Köhne <kai.koehne@qt.io>
commit timeTue, 21 Apr 2026 07:22:04 +0000