Edit the playbook.yml file by adding the new repository under
"sources", with the branch or branches that should be deployed, and the path
where the antora.yml file is found.
For the site to rebuild when there is an update, you need to add a webhook in the repo. In the Netlify panel, go to Site Settings > Build & deploy > Build hooks, and copy the hook URL. In the repo that is being added, go to Settings > Webhooks, and add a webhook using this URL and the default settings.
To show it in the sidebar, add the name from the repo's antora.yml in
navigation.hbs, and add an svg icon
inside the icons folder matching the name.
Finally, add an entry for it inside the model.yml file, for UI development purposes.