Update README.md to mention experimental ZiGate support (#204)

Update README.md to mention experimental ZiGate support plus links to code/library and hardware.

This replaces #115

@doudz has now publish zigpy-zigate v0.1.0 which has experimental support for ZiGate to Zigpy

https://github.com/doudz/zigpy-zigate

zigpy-zigate 0.1.0 release on PyPI

https://pypi.org/project/zigpy-zigate/#history

Requires ZiGate firmware 3.1a or later firmware version which has added a raw mode

https://zigate.fr/tag/firmware/

README.md

@@ -23,5 +23,9 @@ zigpy works with separate radio libraries which can each interface with multiple
   - [ConBee](https://www.dresden-elektronik.de/conbee/) USB adio adapter from [Dresden-Elektronik](https://www.dresden-elektronik.de)
   - [RaspBee](https://www.dresden-elektronik.de/raspbee/) GPIO radio adapter from [Dresden-Elektronik](https://www.dresden-elektronik.de)
 
-  **Related projects:**
-  ZHA deviation handling in Home Assistant relies on on the third-party [ZHA Device Handlers](https://github.com/dmulcahey/zha-device-handlers) project. Zigbee devices that deviate from or do not fully conform to the standard specifications set by the [Zigbee Alliance](https://www.zigbee.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 component in Home Assistant. These ZHA Device Handlers for Home Assistant can thus be used to parse custom messages to and from non-compliant Zigbee devices. The custom quirks implementations for zigpy implemented as ZHA Device Handlers for Home Assistant are a similar concept to that of [Hub-connected Device Handlers for the SmartThings Classics platform](https://docs.smartthings.com/en/latest/device-type-developers-guide/) as well as that of [Zigbee-Shepherd Converters as used by Zigbee2mqtt](https://www.zigbee2mqtt.io/how_tos/how_to_support_new_devices.html), meaning they are each virtual representations of a physical device that expose additional functionality that is not provided out-of-the-box by the existing integration between these platforms.
+**Experimental Zigbee radio modules:**
+- ZiGate based radios (via the [zigpy-zigate](https://github.com/doudz/zigpy-zigate) library for zigpy)
+  - [ZiGate open source ZigBee adapter hardware](https://zigate.fr/)
+
+**Related projects:**
+ZHA deviation handling in Home Assistant relies on on the third-party [ZHA Device Handlers](https://github.com/dmulcahey/zha-device-handlers) project. Zigbee devices that deviate from or do not fully conform to the standard specifications set by the [Zigbee Alliance](https://www.zigbee.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 component in Home Assistant. These ZHA Device Handlers for Home Assistant can thus be used to parse custom messages to and from non-compliant Zigbee devices. The custom quirks implementations for zigpy implemented as ZHA Device Handlers for Home Assistant are a similar concept to that of [Hub-connected Device Handlers for the SmartThings Classics platform](https://docs.smartthings.com/en/latest/device-type-developers-guide/) as well as that of [Zigbee-Shepherd Converters as used by Zigbee2mqtt](https://www.zigbee2mqtt.io/how_tos/how_to_support_new_devices.html), meaning they are each virtual representations of a physical device that expose additional functionality that is not provided out-of-the-box by the existing integration between these platforms.