Merge pull request #48076 from joncojonathan/update-CONTRIBUTING_cp

CONTRIBUTING.md: add clarification on periods in commit messages

.github/CONTRIBUTING.md

@@ -20,6 +20,8 @@ under the terms of [COPYING](../COPYING), which is an MIT-like license.
   (Motivation for change. Additional information.)
   ```
 
+  For consistency, there should not be a period at the end of the commit message.
+
   Examples:
 
   * nginx: init at 2.0.1