Add link to docs

homeassistant/components/group.py

 """
 homeassistant.components.group
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-
 Provides functionality to group devices that can be turned on or off.
-"""
 
+For more details about this component, please refer to the documentation at
+https://home-assistant.io/components/group.html
+"""
 import homeassistant.core as ha
 from homeassistant.helpers import generate_entity_id
 from homeassistant.helpers.event import track_state_change