Any publicity efforts for this site need to explain two things: What Stack Exchange Q&A is, and why Writers is a good site. We faced this issue a while back on Bicycles. I've taken some of the text there and adapted it for this site. Please feel free to edit and tweak!
Note that this is designed to be modular: You can use the first paragraph on its own, or the entire thing. Useful when you have limited space on a flyer!
(Of course, this is just a starting point!)
Writers.stackexchange.com is the no-nonsense Writers' enthusiast Q&A built by users. Instead of wading through a lot of random discussion to get to the good stuff, the best answers are always voted to the top!
Writers is one of many sites on the Stack Exchange network that synthesizes the best aspects of wikis, blogs, and forums, in a way that results in almost all questions getting great answers, often stunningly quickly. You don’t have to register, but if you do, you collect reputation points for your great answers and establish yourself as a top writing expert! The site covers fiction, non-fiction, editing, style issues, and more. Writers, editors, agents, and other writing professionals will find the site a great resource.