Fix url in Service Desk How-To docs

What does this merge request do and why?

A minor tweak to the docs for usability.

1. The url specifies <gdk-root>/log/, the logs are actually in the <gdk-root>/gitlab/log folder.
2. Change: Move the mention of the gdk-root folder out of the code block and into the line above, to match the other usages in the same readme doc.
3. This also makes it possible to copy-paste the command and run it directly 👍🏻

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

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.