Update contributing guidelines

CONTRIBUTING.md

@@ -3,12 +3,21 @@
 Contributions to the RapidPro projects are highly appreciated! 
 
 We accept contributions in the form of:
- * bug reports 
- * pull requests for code changes
- * documentation updates
+ * Bug reports 
+ * Pull requests for code changes
+ * Documentation updates
 
-All non-trivial pull requests, especially those with functional changes should first open a ticket to discuss approach and likelyhood of inclusion in the project.
+All non-trivial pull requests, especially those with functional changes should first open a ticket to discuss approach 
+and likelihood of inclusion in the project.
 
-Note that all pull requests must maintain 100% unit test coverage (without new no-covers) and pass all unit tests.
+Note that all pull requests must:
 
-RapidPro is licensed under the AGPL-3.0 and your contributions will be licensed in the same way. Note that contributing does not change your rights to use your own Contributions for any other purpose.
+ * Pass all unit tests
+ * Maintain 100% unit test coverage (without new no-covers)
+ * Pass the code quality checks (flake8 etc)
+
+There is a script called `code_check.py` in the root of the repository which you can run to ensure that your PR will
+pass the checks configured in our CI.
+
+RapidPro is licensed under the AGPL-3.0 and your contributions will be licensed in the same way. Note that contributing 
+does not change your rights to use your own Contributions for any other purpose.