Additional documentation needed for docker installation

[terrillmoore]

Please add a link to https://docs.docker.com/engine/install/ in README.md, so that people know where to go for instructions. Typically, docker install is not really handled properly by the distribution package manager, and you need to follow the instructions at docker.com for a satisfactory installation.

It would also be nice for the Makefile to check prerequisites and print a message (or point to the README) about what you might want to do if prerequisites are missing.

Also, both the README and the Makefile should point out that if you've just installed Docker, you need to make sure you're in the docker group (adduser, and logout/log in to be sure). Again, it's not hard for the Makefile to check whether you're in the docker group and prompt & exit if not.

[jchonig]

I can update the README.md with instructions to install docker. And probably update the Makefile to check for prerequisites.

However, the Makefile is now designed to only run under bin/run, so it should only be running inside a docker container.

[terrillmoore]

Normally I run makefiles outside docker, and call docker run. That way, the makefile can build the containser etc. It's easy to do docker run and launch a specific ansible command. (Though the command gets long.)