Add statement to CONTRIBUTING.md about update of APIs (#2695)

CONTRIBUTING.md

@@ -44,6 +44,7 @@ After you've created a branch on your fork with your changes, it's time to [make
 
 ## Pull Request Guidelines
 
+* Never put an update/new version of an API that is already listed, the old version of the API gets deprecated.
 * Continue to follow the alphabetical ordering that is in place per section.
 * Each table column should be padded with one space on either side.
 * The Description should not exceed 100 characters.