Add a CocoaPods badge to the README

Author: solidcell

README.md

@@ -1,5 +1,6 @@
 RxSwiftUtilities
 ======================================
+[![CocoaPods Compatible](https://img.shields.io/cocoapods/v/RxSwiftUtilities.svg)](https://img.shields.io/cocoapods/v/RxSwiftUtilities.svg)
 [![Carthage Compatible](https://img.shields.io/badge/Carthage-compatible-4BC51D.svg?style=flat)](https://github.com/Carthage/Carthage)
 
 ## About