Merge pull request #382 from pusher/update-badge

Add CocoaPods badge to README

Author: fbenevides

README.md

@@ -3,6 +3,7 @@
 ![Build Status](https://app.bitrise.io/app/3c6dac112b98e7fe.svg?token=n0z-aWua_Bc35kUGu4qpYg)
 [![codecov](https://codecov.io/gh/pusher/pusher-websocket-swift/branch/master/graph/badge.svg)](https://codecov.io/gh/pusher/pusher-websocket-swift)
 [![Latest Release](https://img.shields.io/github/v/release/pusher/pusher-websocket-swift)](https://github.com/pusher/pusher-websocket-swift/releases)
+[![CocoaPods](https://img.shields.io/cocoapods/v/PusherSwift)](https://img.shields.io/cocoapods/v/PusherSwift)
 [![API Docs](https://img.shields.io/badge/Docs-here!-lightgrey)](https://pusher.github.io/pusher-websocket-swift/)
 [![Supported Platforms](https://img.shields.io/endpoint?url=https%3A%2F%2Fswiftpackageindex.com%2Fapi%2Fpackages%2Fpusher%2Fpusher-websocket-swift%2Fbadge%3Ftype%3Dplatforms)](https://swiftpackageindex.com/pusher/pusher-websocket-swift)
 [![Swift Versions](https://img.shields.io/endpoint?url=https%3A%2F%2Fswiftpackageindex.com%2Fapi%2Fpackages%2Fpusher%2Fpusher-websocket-swift%2Fbadge%3Ftype%3Dswift-versions)](https://swiftpackageindex.com/pusher/pusher-websocket-swift)