Add examples for cdw under public_cloud/aws

[rjendoubi]

I used to be able to just specify the top-level key dw: in my definition.yml, with no content, in order to get a default CDW Environment spun up. As of today, that fails because "worker subnets not provided".

Which makes sense, but it would be nice if we had an easy reference for what the required options & valid values are 🙂