Add .gitlab-ci.yml
Created by: polyzen
Our GitLab instance doesn't have Pages set up, so I'm using gitlab.com for hosting builds currently: https://polyzen.gitlab.io/asknot-ng
Also enables demoing branches/merge requests, eg. this build of @sonuishaq67's theme changes: https://polyzen.gitlab.io/-/asknot-ng/-/jobs/837122055/artifacts/public/index.html