clarify owned_by docstring

app/models/objective.py

@@ -26,7 +26,7 @@ class Objective(db.Model):
         self.hash = token_hex(16)
 
     def owned_by(self, user):
-        '''given user is an owner of a game object is part of'''
+        '''Returns True if given user is an owner of a game object is part of'''
         return user in [gameplayer.user for gameplayer in self.game.players if gameplayer.role == Role.owner]
 
 class ObjectiveMinimalEncoder(JSONEncoder):