Add .gitlab-ci.yml example

[Jackbennett]

Hey, I'm stuck waiting for pages to be generated with the authorization file in place to continue, but because the job is waiting it isn't continuing on to actually build the site for pages.

Whats some example setups to trigger things in the correct order?

[AntonOfTheWoods]

@Jackbennett , see https://github.com/rolodato/gitlab-letsencrypt/issues/40#issuecomment-419620627