Change section title

CONTRIBUTING.md

@@ -39,8 +39,8 @@ These checks will:
 
 The checks will rerun anytime the PR branch is updated.
 
-Schema Versioning Overview
---------------------------
+Schema Versioning
+-----------------
 
 Individual schemas may have their own internal [version](https://felis.lsst.io/user-guide/model.html#schema-version) for tracking changes, which is defined at the top of the file, as in [apdb.yaml](yml/apdb.yaml).
 (This is distinct from tags or versions of sdm_schemas itself, and not all schemas may be using internal versions.)