Create setup.py and improve install instructions

Currently, there is no direct way of installing PacmanRL easily. You need to clone the repo, download all the tools necessary for building, and the final exported bindings lib.so file for Python is not directly importable (i.e. needs to be imported from the `build/` directory or wherever you decide to move it). A setup.py file that handles the installation/building by running `python3 setup.py [develop|build|install]` will be very useful here.

Updates to the README with proper install instructions for different OS will also be really helpful.

Probably helpful resource: https://gist.github.com/hovren/5b62175731433c741d07ee6f482e2936