Add warning about GenAI code generation (#7098)

We need to tell users about the policy regarding code created by AI tools.

Author: mhucka

CONTRIBUTING.md

@@ -20,6 +20,13 @@ You generally only need to submit a CLA once, so if you've already submitted one
 (even if it was for a different project), you probably don't need to do it
 again.
 
+> [!WARNING]
+> Please note carefully clauses [#5](https://cla.developers.google.com/about/google-corporate#:~:text=You%20represent%20that%20each%20of%20Your%20Contributions%20is%20Your%20original%20creation)
+> and [#7](https://cla.developers.google.com/about/google-corporate#:~:text=Should%20You%20wish%20to%20submit%20work%20that%20is%20not%20Your%20original%20creation%2C%20You%20may%20submit%20it%20to%20Google%20separately)
+> in the CLA. Any code that you contribute to this project must be **your**
+> original creation. Code generated by artificial intelligence tools **does
+> not** qualify as your original creation.
+
 ## Pull Request Process and Code Review
 
 All submissions, including submissions by project members, require review. We