Update zha.markdown to mention recently added group support (#12750)

Add mentioning of device grouping support into entities since a it has been a highly requested feature popularized by the Philips Hue Bridge (with its "light groups") that has been missing from the ZHA integration component and was just recently added via all these pull requests:

https://github.com/home-assistant/frontend/pull/4384
https://github.com/home-assistant/frontend/pull/4382
https://github.com/home-assistant/frontend/pull/4466
https://github.com/home-assistant/frontend/pull/4380
https://github.com/home-assistant/frontend/pull/4376
https://github.com/home-assistant/frontend/pull/4365
https://github.com/home-assistant/core/pull/33196
https://github.com/home-assistant/core/pull/33207
https://github.com/home-assistant/core/pull/33291
https://github.com/home-assistant/core/pull/28823
https://github.com/home-assistant/core/pull/29641
https://github.com/home-assistant/core/pull/30183
https://github.com/home-assistant/core/pull/30433
https://github.com/home-assistant/core/pull/33378
https://github.com/home-assistant/core/pull/31260

source/_integrations/zha.markdown

@@ -33,6 +33,8 @@ There is currently support for the following device types within Home Assistant:
 - Sensor
 - Switch
 
+There is also support for grouping of lights, switches, and fans (i.e. support for commanding device groups as entities).
+
 ## ZHA exception and deviation handling
 
 Zigbee devices that deviate from or do not fully conform to the standard specifications set by the [Zigbee Alliance](https://zigbeealliance.org) may require the development of custom [ZHA Device Handlers](https://github.com/dmulcahey/zha-device-handlers) (ZHA custom quirks handler implementation) to for all their functions to work properly with the ZHA integration in Home Assistant. These ZHA Device Handlers for Home Assistant can thus be used to parse custom messages to and from Zigbee devices.