Merge branch '515978-update-the-remove-blobs-documentation' into 'master'

Resolve "Update the Remove Blobs documentation"

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/184217



Merged-by: Brendan Lynch <blynch@gitlab.com>
Reviewed-by: Brendan Lynch <blynch@gitlab.com>
Co-authored-by: Pranav Jain <pjain@gitlab.com>

doc/user/project/repository/repository_size.md

@@ -172,7 +172,9 @@ To remove blobs from your repository:
 1. Select **Yes, remove blobs**.
 1. On the left sidebar, select **Settings > General**.
 1. Expand the section labeled **Advanced**.
-1. Select **Run housekeeping**.
+1. Select **Run housekeeping**. Wait at least 30 minutes for the operation to complete.
+1. In the same **Settings > General > Advanced** section, select **Prune unreachable objects**.
+   This operation takes approximately 5-10 minutes to complete.
 
 #### Get a list of object IDs