update RESPONSE.md

doc/RESPONSE.md

@@ -13,6 +13,9 @@
 ### iOS
 在你的`AppDelegate`中重写下面方法：
 ```objective-c
+- (BOOL)application:(UIApplication *)application handleOpenURL:(NSURL *)url {
+    return [WXApi handleOpenURL:url delegate:[FluwxResponseHandler responseHandler]];
+}
 
 - (BOOL)application:(UIApplication *)app openURL:(NSURL *)url options:(NSDictionary<NSString*, id> *)options
 {