Clarification that cookieParser and CookieParser(secret) are actually required

I and a few other folks over at https://github.com/strongloop/express/issues/1859 expressed our concern about the documentation for cookieParser() and cookieParser(secret) not making sense. As it currently reads, it implies that when cookieParser() *isn't* used, that's when you get cookie information, whereas the opposite is actually true. 

I hope you like our proposed solution.