Adding Gitlab continuous build instructions

[costrouc]

I have been using gitlab for testing that my binder images build properly and work with mybinder. Would a pull request with information on how to automate it with Gitlab continuous integration be welcome?

An example is here

[betatim]

I think this would be nice.

One thing that is worth thinking about: how do we test that the gitlab CI setup (still) works?

[costrouc]

It would be possible https://docs.gitlab.com/ee/ci/ci_cd_for_external_repos/github_integration.html

Though I have never done it myself.

[betatim]

Ok, let's try and set that up as part of the PR that enables GitLab CI I would say.