taking a stab at porting over the FAQ from wikidot

Left most of it the same, but changed a few relevant details.
What about saying lots of people do and making a list of companies we know instead?

* GitHub (not sure if they still do)
* Vimeo
* Booking.com
* Etsy (I think?)
* Daemonware
* …

And deprecate that page while we're at it: http://graphite.readthedocs.org/en/latest/who-is-using.html