Clean up the configuration settings docs

Verbatim

"The need of changing the gitlab.rb file is quite awkward"

GitLab tier

Self-managed Core (your org's domain)

SUS score

60

More info

The mentioned page is https://docs.gitlab.com/omnibus/settings/configuration.html. Searching for gitlab.rb, there are at least 5 notes/caveats.

An example note that is hard to understand for a new-to-GitLab user and possibly understood but awkward for an experience GitLab person is the following

Screen_Shot_2020-12-03_at_11.00.27_PM

What does after sign out a path mean?

Another one is

Screen_Shot_2020-12-03_at_11.03.46_PM

Have we really had something experimental since 8.5 and is it still experimental?

Edited by Achilleas Pipinellis