You need to make sure that elm 0.19.0 version is install, if it's not just type the next command (may need to be run as sudo):
npm install -g elm@0.19.0
At the root of the repository, type the command bellow, it will install elm dependencies:
elm make
After that you're ready to play by using the following last command:
elm reactor
Open you browser on http://localhost:8000/src/Main.elm to play !