Connect theme from github.

Hi guys, I want to make a project (plugin) that allows me to connect branches of repositories from GitHub like Shopify allowing we for the develop themes super custom with a base clean and the capability to connect with Guthenber. The help I need is a guide on how to register a new theme into the database of WordPress and this theme then connected can be activated. Take into consideration that the connection with GitHub already is. Just I missed registering the theme to be recognized as a wonderful theme. Thanks a lot