Improve CI intro docs

We should continue the work to improve the introductory CI/CD docs, especially the getting started page, and potentially the "Your first pipeline" tutorial.

The following discussion from !128450 (merged) should be addressed:

• @sselhorn started a discussion: (+4 comments)

  I feel like this sentence doesn't actually convey any information.

  The following few sentences don't help much either.

  That said, I think we should merge this MR as an MVC, hide this page down in the nav somewhere, and consider deleting or redirecting it at some point soon.