add docstring to new function

Author: cristiancavalli

chatbase/facebook_user_message.py

@@ -67,6 +67,7 @@ def to_json(self):
         }, default=lambda i: i.__dict__)
 
     def to_set_format(self):
+        """Return a dictionary version of the message for a set"""
         self.set_chatbase_fields()
         return {
             'sender': self.sender,