[CentOS-promo] SIG flyers

To a large extent, the SIGs are what make CentOS interesting, and are one of the primary things that I'd like to see us talking about when CentOS is at events.

To that end, I'd like to create some flyers - half-page docs - that we can have at events, describing what each (active) SIG does, how to get involved, and how to consume what it produces.

I want to start with a flyer that describes SIGs in general, and then make a template that the various SIGs can fill in with relevant information.

I will be attempting to have the main SIG flyer, and several of the individual SIG ones, in time for the Dojo at ORNL in April.

Help enthusiastically welcomed.