Document how to deploy Riju on a single host

[raxod502]

It's possible to run Riju outside of AWS. It's just that you lose the ability to do blue/green deployments and the ability to build the Docker images on a separate host from where you're running the production server, and the ability to run multiple replicas and balance traffic across them.

See https://github.com/raxod502/riju/issues/115 for some discussion on this.

This issue is to track adding documentation to Riju (and maybe an extra Makefile target or two) about what steps are required to build and deploy Riju onto your own server, without using the AWS infrastructure that I've set up for my own deployment.