README Cleanup

@nseidle - yet another readme cleanup.

For this one I borrowed the same product versions section used in others like the Danger Shield to provide links to both the retail and OEM versions we offer. Not sure if that's necessary, but there it is.

I also clarified a point about licenses - before the README described the hardware as CC by SA 3.0 and *everything* as Beerware, presenting a conflict. The language now keeps the CC license on the hardware and describes *everything else* as Beerware.