Fix documentation for kube with private network

[schferbe]

Description

Fixes some issues in the documentation for setting up managed Kubernetes with a private network (vRack).

Type of change

• Documentation update

How Has This Been Tested?

I have a private project where I wanted to set up managed Kubernetes with vRack. It worked after these adjustments.

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings or issues
• I have added acceptance tests that prove my fix is effective or that my feature works
• New and existing acceptance tests pass locally with my changes
• I ran succesfully go mod vendor if I added or modify go.mod file

[amstuta]

Thanks for your contribution :)