Doc/add ai policy pointer (#14037)

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

Author: sametSeckiiin

doc/development/contributing.rst

@@ -5,6 +5,10 @@ Contributing guide
 
 .. highlight:: console
 
+.. important::
+   **AI Usage Policy:** Before submitting any code or documentation, please make sure to review our AI usage policy outlined in the repository `CONTRIBUTING.md file <https://github.com/mne-tools/mne-python/blob/main/CONTRIBUTING.md>`_.
+
+   
 Thanks for taking the time to contribute! MNE-Python is an open-source project
 sustained mostly by volunteer effort. We welcome contributions from anyone as
 long as they abide by our `Code of Conduct`_.