documentation: Adding more documentations for users new to harvester and how to properly set up harvester

[PatrickLaabs]

Describe the solution you'd like:
Since I am fairly new to harvester, I had some troubles to get it up and running in the first place.

Why do you want this feature:
As a user, I'd like to have a quick and easy to read documentation about how to set up a brand new harvester instance.

Things like:

• Adding the SSH Key
• Getting the Kubeconfig of the Harvester Cluster
• Creating the needed Network

etc.

Anything else you would like to add:
If this is something useful, I'd like to add this kind of documentation to this provider.
I guess it could be helpful for new folks - like me - to get up and running a lot faster and start using this awesome provider 😄

[belgaied2]

@PatrickLaabs if you are still willing to contribute this doc, I would more than happy to review it.