Split developer and user docs, extending install and upgrade docs

This PR is a substantial reworking of the existing document. It's also splits the developer docs from the user docs.

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #554
| Refs tickets  | 
| License       | MIT
| Doc PR        |