docs: add CONTRIBUTING.md file

Signed-off-by: Gabriele Bartolini <gabriele.bartolini@enterprisedb.com>

Author: gbartolini

CONTRIBUTING.md

@@ -0,0 +1,10 @@
+# Contributing to CloudNativePG
+
+Thank you for your interest in contributing! 💖
+
+To ensure consistency across the project, all CloudNativePG repositories follow
+a common set of guidelines regarding code of conduct, AI usage, and
+contribution workflows.
+
+Please review the [CloudNativePG Project contributing guidelines](https://github.com/cloudnative-pg/governance/blob/main/CONTRIBUTING.md)
+before searching for issues, reporting bugs, or submitting a pull request.