All you need to do to publish your add-on is host it publically, and have the endpoint field in your manifest to point to the HTTP URL where the add-on is accessible (e.g. http://twitch.strem.io).
Hosting the add-on is very easy, since Stremio add-ons are simply Node.js applications. You can see - hosting your Add-on tutorial.
When you have a publically hosted add-on, and the endpoint field is properly set, the stremio-addons module will send the information about the add-on to our API, and it will automatically evaluate if your add-on is accessible and if so, it will be shown in our Add-on catalogue. We do not moderate the listing on (https://addons.strem.io), the add-on should show automatically once endpoint is pointed to a valid endpoint.
Please note that in order for the add-on to work on Android and iOS, it needs to support the https protocol. It's not necessary that you will use https. However, the mobile application will always try to access it through https.