Enable dat dashboard

Yo, few changes here to get to a working vanilla install with the dashboard. Highlights:

* Dashboard config taken from riemann-dash examples
* Install a ruby specifically for riemann (which unfortunately still requires `ruby_build` in the run list)
* Runit templates
* Small README update

Still needs to be quite a bit more dynamic, some LWRP love, etc. but it's a good start. Actually, a bit unsure about the runit dashboard situation, but I think that's more a rubby problem. More than anything I just want a checkin point.