Add Docker support

[pataquets]

Add Dockerfile to enable image building. Useful for development and tests under Docker workflow.
Using the official Python 3 image, latest tag. More info at https://hub.docker.com/_/python/

Just adding files, setting working dir and running install and build instructions.

Build:

$ docker build -t dlnap .

Run:

$ docker run --rm -it dlnap [options...]

FYI, there's a still quicker to test, already built image on my Docker Hub. Test it by running:

$ docker run --rm -it pataquets/dlnap [options...]

Using --rm causes container it to be deleted after stop and -it makes the container not to go background and run interactively.

Optional improvement to come (maybe in another issue):

• Create an 'official', based on your repo, automated build at Docker Hub for the image: https://docs.docker.com/docker-hub/builds/ . Just requires a free paid Docker Hub account and a following a quick 'Create automated build' process. I'll be happy to help on it, if needed.

[pataquets]

@cherezov Do you have any feedback about this?