Add how-to page to compile a cluster

[ccremer]

• Adds a dedicated how-to page to compile clusters including setting environment variables.

Checklist

• [x] Keep pull requests small so they can be easily reviewed.
• [x] Update the documentation.

[ccremer]

LGTM, but I'm not sure this needs to be separate from "Change a parameter".

They're very similar indeed. I could update the change-parameter guide so it builds on top of compile-catalog.