Add offical self-hosting instructions

[syeopite]

Expected behavior

For official instructions on self hosting to exist.

Actual behavior

There doesn't seem to be any instructions for self hosting at the moment. The requirement of Postgres, Redis and Amazon S3 are all unknown to those who wants to host their own instance of notebook. There's also a lack of information on how to configure it, instead often requiring users to search through the issues of this repo.

Would it be possible to add official self hosting instructions?

[drusepth]

Started work on this in the Setup instructions wiki page. Still needs fleshing out in a few more places, but if anyone has questions or other problems I'll start collecting them there for everyone to benefit from. 👍