Add CONTRIBUTING.md file


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

Change-Id: I9bfb76385b254d4d643739715cecd8037a8fff37
Reviewed-by: André Hartmann <aha_1980@gmx.de>
commit8e5d51d2cd9b7b6542ebcec7ee9a6bfa7f7fb96f
parent223a5bd4359d061e64d687b01c1a84683a7f2601
authorKai Köhne <kai.koehne@qt.io>
committerKai Köhne <kai.koehne@qt.io>
commit timeTue, 21 Apr 2026 14:34:11 +0000