Update FAQ for Express 3 support

Adds a simple wrapper to the FAQ for those wishing to use Streamline with Express 3 (https://github.com/aseemk/express-streamline only works with Express 2). Not battle-tested, but it's simple and and hackable, and because it doesn't monkey-patch Express but uses a wrapper function, it allows a Streamline function to be used as middleware and call `next()`.