Add in release notes

Author: AustinBenoit

release_build_files/readme.md

@@ -613,6 +613,11 @@ workflow use only during the development of your app, not for publicly shipping
 code.
 
 ## Release Notes
+
+### Upcoming
+-   Changes
+    - App Check: Add in support for Limted Use Tokens.
+
 ### 13.3.0
 -   Changes
     - General (Android): Update to Firebase Android BoM version 34.6.0.