Added comments in the demo scripts

- Added comments for Api description on App message demo scripts
- Added description in the readme

Assets/HuaweiServiceDemo/Scripts/test/appmessage/AppMessageListener.cs

         }
     }
     
+    // Callback for a message tap.
     public class ClickListener : AGConnectAppMessagingOnClickListener
     {
         public override void onMessageClick(AppMessage arg0)
     }
 
+    // Callback for message closing.
     public class DismissListener : AGConnectAppMessagingOnDismissListener
     {
         public override void onMessageDismiss(AppMessage arg0, AGConnectAppMessagingCallback.DismissType arg1)
         }
     }
 
+    // Callback for message display.
     public class DisplayListener : AGConnectAppMessagingOnDisplayListener
     {
         public override void onMessageDisplay(AppMessage arg0)
         }
     }
 
+    // Callback for message loading exceptions.
     public class OnErrorListener : AGConnectAppMessagingOnErrorListener
     {
         public override void onMessageError(AppMessage arg0)

README.md

 
 The following Kits included.
 - HMS
+    - Game Service
     - Ads
     - Push
     - Location
     - Crash
     - Auth Service
     - Cloud Functions
+    - Cloud Storage
+    - Cloud DB
 
 ***Unity 2019 or higher***
 ***Before build, add your keystore, create huawei agc project and put `agconnect-services.json` under `Assets/Plugins/Android/`***