After installing Elixir, all you have to do is to cd into this folder and then type the following commands in a terminal:
mix deps.get
mix run
You will be greeted by a prompt that will help you do your checkout.
The products and discounts are very configurable, so by default we will try to read the configuration from the file products_config.json, but you can override that by exporting the PRODUCTS_FILE_LOCATION environment variable and pointing it to another file.
It's important that the new file's schema matches the old one, otherwise the app won't work.