Adds Register library for testing Play Store billing

Author: Aritra Roy

README.md

@@ -279,6 +279,7 @@ Remixer is a framework to iterate quickly on UI changes by allowing you to adjus
 * [Parceler](https://github.com/johncarl81/parceler) - Android Parcelables made easy through code generation
 * [PermissionsDispatcher](https://github.com/hotchemi/PermissionsDispatcher) - Simple annotation-based API to handle runtime permissions
 * [ProtoBuf](https://github.com/google/protobuf) - Protocol Buffers - Google's data interchange format
+* [Register](https://github.com/NYTimes/Register) - Android Library and App for testing Play Store billing
 * [Reprint](https://github.com/ajalt/reprint) - A unified fingerprint library for Android
 * [Secure Preferences](https://github.com/scottyab/secure-preferences) - Android Shared preference wrapper than encrypts the values of Shared Preferences
 * [Sensey](https://github.com/nisrulz/sensey) - Detecting gestures in a snap