PYTHON-5118 - Improve contributing documentation of synchro (mongodb#2139)

Author: NoahStapp

CONTRIBUTING.md

@@ -261,6 +261,11 @@ To prevent the `synchro` hook from accidentally overwriting code, it first check
 of a file is changing and not its async counterpart, and will fail.
 In the unlikely scenario that you want to override this behavior, first export `OVERRIDE_SYNCHRO_CHECK=1`.
 
+Sometimes, the `synchro` hook will fail and introduce changes many previously unmodified files. This is due to static
+Python errors, such as missing imports, incorrect syntax, or other fatal typos. To resolve these issues,
+run `pre-commit run --all-files --hook-stage manual ruff` and fix all reported errors before running the `synchro`
+hook again.
+
 ## Converting a test to async
 The `tools/convert_test_to_async.py` script takes in an existing synchronous test file and outputs a
 partially-converted asynchronous version of the same name to the `test/asynchronous` directory.