Fedora CoreOS PRD draft

Recently we hashed out some basic use cases we’d like to support with Fedora CoreOS. I took these and a previous PRD from the Fedora Atomic working group and created a draft PRD for the CoreOS Working Group.

You can open up pull requests for comments or suggested changes to the
PRD by editing the source issue tracker git repo.

As always we can discuss any details at the next meeting on Wednesday.