Update the install guide

[pjc09h]

No description provided.

[pjc09h]

On second thought, I may just pull the install guide and move the API docs over to some free OpenAPI parser, when the API has a set of good models with CRUD support. This target moves way too fast to realistically maintain an accurate install guide. For example, two of the major dependencies, Sphinx and Memcached, don't even exist in the codebase any more. Between the published configs, the source code, and the Slack support channel, there are enough resources out there.

[pjc09h]

Actually, on third thought, I refer to this document semi-frequently. It should be a lot more sparse, e.g., core dependencies listed, certain gotchas documented, links to the relevant configurations, and nothing else.