Update autoscaling documentation
What does this MR do?
Closes #2994 (closed) - This is my first PR to GitLab, I hope it's fine
Moving docs to a new location?
- Make sure the old link is not removed and has its contents replaced with a link to the new location.
- Make sure internal links pointing to the document in question are not broken.
- Search and replace any links referring to old docs in GitLab Runner's source code