Add CONTRIBUTING.md file


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

Change-Id: I7504a8eb77bd91dd5f0fb37686cdb3451c70a0bb
Reviewed-by: Paul Wicking <paul.wicking@qt.io>
commit993288367429ded28da025aa5ff61e224b4d5e8c
parentf4777a00c6dd9af83e154884e164fe9d74362e2f
authorKai Köhne <kai.koehne@qt.io>
committerKai Köhne <kai.koehne@qt.io>
commit timeTue, 21 Apr 2026 07:21:02 +0000