Go to the Supervisor Panel, select Add-on Store, click the three little dots on the upper right and select Repositories. Now fill the Add repository textbox with https://github.com/Minims/homeassistant-addons/ and click Add.
This repository contains the following add-ons
Publish Somfy Home Alarm as MQTT messages.
Publish Somfy Home Alarm as MQTT messages (dev version).
Many Thanks to schumijo for his work on this addon !