Add link to org-level contribution guidelines to contributing doc (ma…

…stodon#31043)

CONTRIBUTING.md

@@ -11,6 +11,11 @@ You can contribute in the following ways:
 
 If your contributions are accepted into Mastodon, you can request to be paid through [our OpenCollective](https://opencollective.com/mastodon).
 
+Please review the org-level [contribution guidelines] for high-level acceptance
+criteria guidance.
+
+[contribution guidelines]: https://github.com/mastodon/.github/blob/main/CONTRIBUTING.md
+
 ## API Changes and Additions
 
 Please note that any changes or additions made to the API should have an accompanying pull request on [our documentation repository](https://github.com/mastodon/documentation).