Docker rails

Hey everyone - I'm submitting this PR to get some early feedback. I'm wondering if the post is clear and has a flow to it. It's quite hard to explain the setup since there is a ton of moving parts just for a basic infrastracture. Also, a lot of the setup is repeated per container so I did my best to skip things that were already mentioned in the post.

Who knew devops could be so complicated? :dancer: 
It could use a service to start it if that's how you set it up :) We are running services in containers which are just a jail (sandboxed resources) so you do all the things as if you were not in a container.

I chose to start postgres explicitly since you can specify the configs.