Improvements to Windows setup

1. The current structure and phrasing caused several students to try
   to either only install the SWC Windows installer, or try to install
   it before installing one one of it's dependencies.

2. We discovered an edge case where a user tried to run the
   installer without an internet connection which causes an error
   since nano can't be downloaded.
Merge pull request #409 from ethanwhite/windows-setup-cleanup

Improvements to Windows setup