Add support for emoji_added message type

discord/flags.py

@@ -371,6 +371,15 @@ class SystemChannelFlags(BaseFlags):
         """
         return 32
 
+    @flag_value
+    def emoji_added(self):
+        """:class:`bool`: Returns ``True`` if the system channel is used for
+        emoji added notifications.
+
+        .. versionadded:: 2.7
+        """
+        return 256
+
 
 @fill_with_flags()
 class MessageFlags(BaseFlags):