Merge branch...

Merge branch '516183-update-parallel-deployments-documentation-to-explain-more-what-this-feature-is' into 'master' 

Update Parallel Deployments documentation to explain more what this feature is

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/181957



Merged-by: Janis Altherr <jaltherr@gitlab.com>
Approved-by: Arpit Gogia <12347103-arpitgogia@users.noreply.gitlab.com>
Approved-by: Grace Lin <glin@gitlab.com>
Approved-by: Savas Vedova <svedova@gitlab.com>
Approved-by: Suzanne Selhorn <sselhorn@gitlab.com>
Reviewed-by: Marcin Sedlak-Jakubowski <msedlakjakubowski@gitlab.com>
Reviewed-by: Janis Altherr <jaltherr@gitlab.com>
Co-authored-by: Marcin Sedlak-Jakubowski <msedlakjakubowski@gitlab.com>