Added more info links.

Added a link to an [iOS app](https://github.com/AshFurrow/C-41) I wrote using ReactiveCocoa and to [my book](https://leanpub.com/iosfrp). 

I've been hesitant to make this pull request, but Just Spahr-Summer suggested that links to my work might be better off here than the [website](https://github.com/ReactiveCocoa/ReactiveCocoa.github.io/pull/2) we're developing for ReactiveCocoa.