update RESPONSE doc

doc/RESPONSE.md

@@ -37,6 +37,8 @@ override the following function in`AppDelegate.m`:
 }
 ```
 
+> NOTE:Don't forget to add URL Schema in order to go back to  your app.
+
 ### Flutter
 We can get the reponse from WeChat after sharing and etc:
 ```dart

doc/RESPONSE_CN.md

@@ -36,6 +36,7 @@
   return [WXApi handleOpenURL:url delegate:[FluwxResponseHandler responseHandler]];
 }
 ```
+> 注意：为了能够返回你的app，请不要忘记添加URL Schema。
 
 ### Flutter
 ```dart