Initial pass at paring down runtime docs.

[cloudnautique]

This takes a first pass at removing sections from the runtime docs that will be covered by the SaaS solution. The goal is for these docs to cover installing and running Runtime on a Kubernetes cluster.

This is still a draft. We need to:

• review the top level nav makes sense.
• Write/modify content to align with the messaging of beta launch.
• Prep this to be hosted on runtime-docs.acorn.io
• Reference back to the new docs.acorn.io site where it makes sense.