Add docker environment

[suecharo]

Add a docker environment to run the ipython2cwl itself in the docker container.

$ docker-compose up jupyter-repo2cwl https://github.com/giannisdoukas/ipython2cwl-demo -o .

It is able to run using the above command on the host machine. Because it is mounting /var/run/docker.sock in docker-compose.yml, the image is generated in the host docker environment. Therefore, it is able to execute the following command on the host machine.

$ docker run -p 127.0.0.1:8888:8888 THE_NAME_OF_THE_GENERATED_IMAGE