Link to video new location

The old link to the video was broken, I looked at all the GitLab CI training videos we had in Google Drive and this seems to be the best one.

Reading through all the documentation without trying things out was making it quite difficult to understand, so I interspersed reading the documentation with implementing it.

I am okay with this being merged in its current state but we would need to get some feedback from @ayufan or someone else that has deep knowledge of what needs to be covered to be able to get the full benefit out of GitLab CI. I will make it my responsibility to make sure I get some feedback and make changes, especially to the Advanced section.

cc/ @abuango