Merge branch 'improve-first-contribution-docs' into 'master'

Improve first contribution docs

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/139359



Merged-by: Lee Tickett <ltickett@gitlab.com>
Reviewed-by: Marco Zille <marco.zille@gmail.com>
Reviewed-by: Niklas <mc.taucher2003@gmail.com>
Reviewed-by: Lee Tickett <ltickett@gitlab.com>