Add a certain number of resources to the trade from giver->getter
        :param terrain: resource type, models.Terrain
        :param num: number to add, int
        :return: None

def give(self, terrain, num=1):
        """
        Add a certain number of resources to the trade from giver->getter
        :param terrain: resource type, models.Terrain
        :param num: number to add, int
        :return: None
        """
        for _ in range(num):
            logging.debug('terrain={}'.format(terrain))
            self._give.append(terrain)