Added zigbee channel reference to PTM_215Z.md (#3660)

Author: EmilFlach

docs/devices/PTM_215Z.md

@@ -35,7 +35,7 @@ Not all Zigbee devices can do this translation. The devices known to do this are
 Green Power devices don't support binding and are not included in network scans.
 
 ### Pairing
-Before starting a pairing attempt, please read carefully this section from the **[documentation ](https://www.zigbee2mqtt.io/advanced/zigbee/01_zigbee_network.html#green-power-devices)**
+Before starting a pairing attempt, please read carefully this section from the **[documentation ](https://www.zigbee2mqtt.io/advanced/zigbee/01_zigbee_network.html#green-power-devices)**. Additionally, it's important to know which channel your Zigbee network is using (the default is 11). You can find this in the Zigbee2MQTT frontend under `Settings > Advanced`, or [learn more about changing the channel](https://www.zigbee2mqtt.io/guide/configuration/zigbee-network.html#changing-the-zigbee-channel).
 
 This device has 4 buttons:
 
@@ -48,7 +48,7 @@ This device has 4 buttons:
 
 In case the module is integrated in a single rocker switch, you need to remove the caps to expose all buttons. A button can be pressed by holding the contact of that button and then push the energy bar.
 
-To pair it, hold the corresponding button for that channel for 7 seconds or more.
+To pair it, hold the corresponding button for the channel of your network for 7 seconds or more.
 
 Once the device is paired you need to confirm the channel. To do this press A1 and B0 together. Important: don't press any other buttons between this and the pairing.