Update local path for gdk gitlab dir in docs

What does this merge request do and why?

When I set up my GDK in a box, the proper path was /home/debian/gitlab-development-kit/gitlab, not /home/gitlab-development-kit/gitlab.

How to set up and validate locally

1. Set up the gdk in a box. You will not be able to use /home/gitlab-development-kit/gitlab as the path to open over remove ssh in vscode, as that does not exist. You will need to use /home/debian/gitlab-development-kit/gitlab.

Impacted categories

The following categories relate to this merge request:

• gdk-reliability - e.g. When a GDK action fails to complete.
• gdk-usability - e.g. Improvements or suggestions around how the GDK functions.
• gdk-performance - e.g. When a GDK action is slow or times out.

Merge request checklist

• This change is backward compatible. If not, please include steps to communicate to our users.
• Tests added for new functionality. If not, please raise an issue to follow-up.
• Documentation added/updated, if needed.
• Announcement added, if change is notable.
• gdk doctor test added, if needed.
• Add the ~highlight label if this MR should be included in the CHANGELOG.md.