I do it all manually using the WoWInterface update API:
https://www.wowinterface.com/forums/...ad.php?t=51835
For example, I have my addon zip file ready for uploading in the root of my C drive and run the following in cmd/terminal:
curl -H "x-api-token: <my_token_I_generated_from_wowinterface>" -F "id=<my_addon_id>" -F "version=<new_version_of_my_addon>" -F "compatible=9.0.5" -F "updatefile=@<my_zip_filename.zip>"
https://api.wowinterface.com/addons/update
but if you want to automate it with a packager on GitHub then it's more complicated and someone else can help you with that.