Update troubleshooting section
What does this MR do?
This MR updates the troubleshooting section, as GitLab now (starting from 8.14.0) supports triggering builds on web commits.
Are there points in the code the reviewer needs to double check?
I think it just needs a peer review for wording.
Why was this MR needed?
This MR fixes what is requested by this issue.
What are the relevant issue numbers?
Closes #13479 (closed)