Merge branch 'hhoerl/359825-runner-submodules-docs' into 'master'

Update docs for submodule update flags

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/183183



Merged-by: Roshni Sarangadharan <rsarangadharan@gitlab.com>
Approved-by: Roshni Sarangadharan <rsarangadharan@gitlab.com>
Approved-by: Romuald Atchadé <ratchade@gitlab.com>
Reviewed-by: Romuald Atchadé <ratchade@gitlab.com>
Reviewed-by: Roshni Sarangadharan <rsarangadharan@gitlab.com>
Co-authored-by: Hannes Hörl <hhoerl@gitlab.com>