Moves wiki into main repo to allow for Pull Requests.  Other upgrades to install docs.

Realized that we can't use wikis for Pull Requests (not a built-in feature of GH), so moved everything into this main repo.

We should a) merge this back in to the main SI Org, and then b) re-fork from all other city Orgs to update the content of those install instructions.

I added a bunch of clarifications to each doc, and improved the Virtual Box instructions.  I have an [open issue on the Boston repo](https://github.com/StartupInstituteBoston/DevelopmentInstallWiki/issues/1) to create instructions for Dual Booting on Windows (I didn't have time to get to it).