small correction in comment and constructor

city_model_structure/building.py

@@ -36,6 +36,7 @@ class Building(CityObject):
     self._storeys_above_ground = None
     self._foot_print = None
     self._usage_zones = []
+    self._building_units = []
     self._type = 'building'
     self._monthly_heating = []
     self._monthly_cooling = []
@@ -267,7 +268,6 @@ class Building(CityObject):
     """
     Building units
     :param value: [BuildingUnit]
-    :return: List of building units
     """
     self._building_units = value