Add platform badge to README

Author: solidcell

README.md

@@ -2,6 +2,7 @@ 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)
+[![Platform](https://img.shields.io/cocoapods/p/RxSwiftUtilities.svg?style=flat)](http://cocoadocs.org/docsets/RxSwiftUtilities)
 
 ## About