Add worker docker file

[agomezl]

This docker container allows to start a worker in any machine (with docker installed) by simply doing:

$ docker run -d --name oven1 agomezl/oven

You can check it's output with:

$ docker logs oven1

And stop it with:

$ docker stop oven1
$ docker rm oven1

The idea is to simplify the deployment of workers and allow for better control of resources using docker build-in cgroups functionality, eg:

$ docker run -d -m 16gb --name oven1 agomezl/oven

will limit the workers memory usage to 16gb, neat isn't?

[xrchz]

Would you mind updating the README too? I don't think the Docker approach should be the only or primary method for setting up a worker, but it's a great option to have.

[agomezl]

@xrchz README updated!