Fix heading level for Legal section in CONTRIBUTING.md

Author: yrodiere

CONTRIBUTING.md

@@ -3,7 +3,7 @@
 Contributions from the community are essential in keeping Hibernate (and any Open Source
 project really) strong and successful.  
 
-# Legal
+## Legal
 
 All original contributions to Hibernate are licensed under the 
 [Apache 2.0 license](https://www.apache.org/licenses/LICENSE-2.0).