Improve asdf troubleshooting documentation

What does this merge request do and why?

Improve the onboarding experience for new GDK users by adding more troubleshooting help for asdf. These instructions address a problem that cost me a fair bit of time when initially onboarding.

How to set up and validate locally

Since this only impacts documentation you can preview using the Web IDE

• Edit > Open in Web IDE
• Shift + Command + V to open Markdown preview

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.