Merge branch 'sdejonge-root-scss-discussion-links' into 'master'

Add MR links to root stylesheet comment blocks

See merge request gitlab-org/gitlab!190628



Merged-by: Lukas Eipert <leipert@gitlab.com>
Approved-by: Dan MH <dmizzi-harris@gitlab.com>
Approved-by: Lukas Eipert <leipert@gitlab.com>
Reviewed-by: Scott de Jonge <sdejonge@gitlab.com>
Co-authored-by: sdejonge <sdejonge@gitlab.com>
Co-authored-by: Stanislav Lashmanov <slashmanov@gitlab.com>