Add guide for installing Docker on Ubuntu 16.04 and modify README

Hi

I noticed that the Windows docker guide also contains the instructions for installing Docker on Windows. The current README.md file contains instructions for using the docker image on Ubuntu but not the docker installation steps. I am working on a guide for installing docker and the image on mac OS and thought that the all the 3 guides should have same set of instructions.

1. Installing docker
2. Using the docker image

Also, the current README.md file should be modified to only contain the necessary information about the project and the installation instructions should be kept in README_Ubuntu.md

I can create a PR for the last part first but wanted to know what are the thoughts about this.

Thanks