Add support for running in docker

I have added support in the documentation for how to run wdb for an app running in a docker container. I have also added a `Dockerfile` to the server, so that you can set up Automated Docker builds, for the repository.

For it to create a docker build of the server, on every git push, you would need to set up an account on the docker registry and [add this repo to build](https://registry.hub.docker.com/builds/github/Kozea/wdb/) `Kozea/wdb-server`. 

It should pull from the master branch, with a Dockerfile location in `/server`.

How does that sound?