Creating a Fan Controller Add-On for Gateway RPi Case Cooling Fan

Hi. I have upgraded my RPi 3+ to a RPi 4 with 8GB of memory. Since upgrading the processing hardware, the WebThings Gateway runs HOT, even with a solid and chunky heatsink attached. I’m considering fitting the board into a fan cooled case, with thermostat control ( Argon ONE V2 Case). The Argon script, when installed via SSH, does not seem to work. Is there any documentation which shows how to start creating an Add-On.

If you read the WebThings docs page, there is a section about addons that includes creating an addon. When I wrote my X10 CM15 addon, I just cloned existing ones and merged them together.