Add documentation for Xiaomi CGDK2 (#920)

Co-authored-by: zaluthar <zaluthar@users.noreply.github.com>
Co-authored-by: Jesse Hills <3060199+jesserockz@users.noreply.github.com>

components/sensor/xiaomi_ble.rst

@@ -267,6 +267,31 @@ Configuration example:
         battery_level:
           name: "CGD1 Battery Level"
 
+CGDK2
+*****
+
+Cleargrass (Qingping) Temp & RH Lite, round body, segment LCD, encrypted, broadcasts temperature, humidity and battery status. Requires a bindkey in order to decrypt the received data (see :ref:`obtaining_the_bindkey`).
+The measurements are broadcast every 10-15 minutes.
+
+.. figure:: images/xiaomi_cgdk2.jpg
+    :align: center
+    :width: 30.0%
+
+Configuration example:
+
+.. code-block:: yaml
+
+    sensor:
+      - platform: xiaomi_cgdk2
+        mac_address: "58:2D:34:11:34:B7"
+        bindkey: "fe39106baeedb7c801e3d63c4396f97e"
+        temperature:
+          name: "CGDK2 Temperature"
+        humidity:
+          name: "CGDK2 Humidity"
+        battery_level:
+          name: "CGDK2 Battery Level"
+
 JQJCY01YM
 *********
 
@@ -422,6 +447,13 @@ If the LYWSD03MMC sensor is operated with the Xiaomi stock firmware, you can use
 
     The new bind key will work with ESPHome, but the Mi Home app will not recognise the sensor anymore once the device has been activated by the TeLink flasher application. To use the sensor again with the Xiaomi Mi Home app, the device needs to be removed and then re-added inside the Mi Home app.
 
+CGDK2
+*****
+
+The method to obtain a new bind key for the CGDK2 sensor is similar to the method for the LYWSD03MMC sensor, except a modified version of the flasher application is used.
+
+For this, you load the `application <https://zaluthar.github.io/TelinkFlasher.html>`__ with a `supported browser <https://github.com/WebBluetoothCG/web-bluetooth/blob/master/implementation-status.md>`__ and connect the device by pressing "Connect". After the connection is established, you press the "Do Activation" button and the new key will be shown in the "Mi Bind Key" field. The key can be copied directly into the sensor YAML configuration.
+
 Other encrypted devices
 ***********************
 
@@ -452,5 +484,6 @@ See Also
 - Xiaomi LYWSD03MMC passive sensor readout `<https://github.com/ahpohl/xiaomi_lywsd03mmc>`__ by `@ahpohl <https://github.com/ahpohl>`__
 - Custom firmware for the Xiaomi Thermometer LYWSD03MMC `<https://github.com/atc1441/ATC_MiThermometer>`__
 - TeLink flasher application `<https://atc1441.github.io/TelinkFlasher.html>`__
+- TeLink flasher application modified for CGDK2 `<https://zaluthar.github.io/TelinkFlasher.html>`__
 
 - :ghedit:`Edit`