Include manual downloads badge

Author: aaronschubert0

README.md

@@ -5,6 +5,7 @@
 [![Version](https://img.shields.io/cocoapods/v/AsyncDisplayKit.svg)](http://cocoapods.org/pods/AsyncDisplayKit)
 [![Platform](https://img.shields.io/cocoapods/p/AsyncDisplayKit.svg)]()
 [![License](https://img.shields.io/cocoapods/l/AsyncDisplayKit.svg)](https://github.com/facebook/AsyncDisplayKit/blob/master/LICENSE)
+[![Downloads](https://img.shields.io/badge/downloads-%3E120k-green.svg)](http://cocoapods.org/pods/AsyncDisplayKit)
 
 AsyncDisplayKit is an iOS framework that keeps even the most complex user
 interfaces smooth and responsive.  It was originally built to make Facebook's