The universal patch update guide needs an update

https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/update/patch_versions.md

Doesn't mention gitlab workhorse at all at the moment.
The last update was 1 month ago.
That guide is directly linked on the update page which is linked on every release blog post.
I think we should update it asap :)

/cc @axil @rspeicher