Added some badges to the README

Author: nicolasgarnier

README.md

@@ -1,3 +1,6 @@
+[![npm version](https://badge.fury.io/js/react-firebaseui.svg)](https://badge.fury.io/js/react-firebaseui)
+[![GitHub license](https://img.shields.io/github/license/firebase/firebaseui-web-react.svg)](https://github.com/Firebase/firebaseui-web-react/blob/master/LICENSE)
+
 # FirebaseUI React Components
 
 FirebaseUI React Components provides React Wrappers on top of the [Firebase UI Web library](https://github.com/firebase/firebaseui-web/) and notably Firebase UI Auth.