Merge branch 'add-user-docs-for-user-contribution-mapping' into 'master'

Add user docs for user contribution mapping

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/160763



Merged-by: Evan Read <eread@gitlab.com>
Reviewed-by: Luke Duncalfe <lduncalfe@gitlab.com>
Co-authored-by: Magdalena Frankiewicz <mfrankiewicz@gitlab.com>