I just created a group for Atheists on Branch (www.branch.com). If you haven't heard of Branch, it's a new conversation startup that's backed by the founders of Twitter and Blogger and is trying to bring great offline conversations, like the ones you have around a dinner table, online. Our group will let us start “branches” with each other really easily, and give us a page where we can share them with people and friends can ask to join. It's like the best…