ZHA troubleshooting Zigbee OTA upgrading of device firmware

Add new sections under troubleshooting about resolving ZHA problems with Zigbee OTA upgrading of device firmware not starting or failing.

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@@ -583,6 +583,14 @@ Since all Zigbee Coordinator radio adapters are very sensitive/susceptible to al
   - Place your Zigbee Coordinator away from any Wi-Fi access points and all other sources of WiFi.
   - Wi-Fi frequency ranges can overlap with Zigbee, see the section above on defining Zigbee channel use.
 
+### Problems upgrading Zigbee device firmware via OTA
+
+Be aware that OTAU (Over-The-Air Upgrade) of Zigbee devices typically takes around 10 minutes. While a device is updating a lot of traffic is generated on the network, therefore it is recommended to not execute multiple updates at the same time. Always check that battery-powered devices have at least 70% of battery-life left before starting a firmware upgrade (a general tip is therefore to simply put new fresh batteries in before upgrading any OTA firmware upgrade), OTA updating of firmware is very power-consuming and while some devices do check for a minimum battery-level before starting the upgrade and might refuse to update unless have enough battery-life left, not all do so.
+
+If Zigbee firmware upgrades do not start on a battery-powered product then be aware that you usually need to "wake up the device" so that will will be able to receive commands, (because battery-powered products are sleepy devices so they normally only receive commands when the state of the device is changed). If the upgrade still does not start then try restarting the device by disconnecting the power/battery for a few seconds and try again, again make sure to activate the device by pressing a button on it right before sending the update request. Try to push a button on the device (if it has one) shortly before you start the firmware update to wake it up. Sometimes it also helps to try keeping the device awake by pushing a button repeatedly until you see the first "Updating... " message in the user interface.
+
+Another common reason for Zigbee firmware upgrades not starting or failing is poor reception or not having a stable Zigbee network mesh. Take some basic actions to try to optimize your Zigbee network by avoiding radio frequency interference and adding many Zigbee Router devices (repeaters/extenders) to extend range and coverage. Try to follow all the best practice tips above in the [Zigbee interference avoidance and network range/coverage optimization)](#zigbee-interference-avoidance-and-network-rangecoverage-optimization) section under troubleshooting.
+
 ### Zigbee network visualization in ZHA UI
 
 The ZHA configuration UI has a tab to visualize device links in your Zigbee network topology.