Update release notes for 10.1.0 release (#514)

Author: AlmostMatt

docs/readme.md

@@ -67,10 +67,16 @@ Support
 
 Release Notes
 -------------
-### Upcoming
+### 10.1.0
 - Changes
+    - General: Update to Firebase C++ SDK version 10.1.0.
+    - General (Android): Update to Firebase Android BoM version 31.0.2.
+    - General (iOS): Update to Firebase Cocoapods version 10.1.0.
     - Crashlytics (Android): Fixed an [issue](https://github.com/firebase/quickstart-unity/issues/1116)
       with symbols being stripped when using the tgz package.
+    - Firestore (Android): Reduce the number of JNI global references consumed
+      when creating or updating documents
+      ([#1111](https://github.com/firebase/firebase-cpp-sdk/pull/1111)).
 
 ### 10.0.1
 - Changes