Add a README.md

:bowtie: 
This is also more specific to Commerce 1.x. Nothing in Commerce 2.x at the moment has a dependency on these modules, and some don't even have Drupal 8 versions. Additionally, modules are installed to the root /modules directory now on Drupal 8. I think I'd just say you install a standard installation of Drupal 8, put this project into /modules, and then enable the desired modules from /admin/modules.