Update release notes for 10.7.0 (#663)

* Update release notes for 10.7.0

Author: AlmostMatt

docs/readme.md

@@ -69,8 +69,11 @@ Support
 
 Release Notes
 -------------
-### Upcoming
+### 10.7.0
 - Changes
+    - General: Update to Firebase C++ SDK version 10.7.0.
+    - General (Android): Update Firebase Android BoM dependencies to v31.3.0.
+    - General (iOS): Update Firebase Cocoapods dependencies to v10.7.0.
     - Messaging (Android): Generate the custom MessagingUnityPlayerActivity
       as a Java file instead of precompiling it. This is to better support
       changes with the UnityPlayerActivity, and GameActivity options, in