Hass.io allows anyone to create add-on repositories to share their add-ons for Hass.io easily. This repository is one of those repositories.
Adding this add-ons repository to your Hass.io Home Assistant instance is pretty easy. Follow https://home-assistant.io/hassio/installing_third_party_addons/ on the website of Home Assistant, and use the following URL:
https://github.com/maaad/hassio-addons/