add build status to readme

Author: morganchen12

README.md

@@ -1,5 +1,7 @@
 # FirebaseUI for iOS — UI Bindings for Firebase
 
+[![Build Status](https://travis-ci.org/firebase/FirebaseUI-iOS.svg?branch=master)](https://travis-ci.org/firebase/FirebaseUI-iOS)
+
 FirebaseUI is an open-source library for iOS that allows you to quickly connect common UI elements to the [Firebase](https://firebase.google.com?utm_campaign=Firebase_update_awareness_general_en_05-18-16_&utm_source=?utm_campaign=Firebase_featureoverview_awareness_analytics_en_05-18-16_&utm_source=?utm_campaign=Firebase_announcement_awareness_general_en_05-18-16_&utm_source=Firebase&utm_medium=ads&utm_medium=?utm_campaign=Firebase_announcement_awareness_general_en_05-18-16_&utm_source=Firebase&utm_medium=ads&utm_medium=?utm_campaign=Firebase_update_awareness_auth_en_05-18-16_&utm_source=?utm_campaign=Firebase_announcement_awareness_general_en_05-18-16_&utm_source=Firebase&utm_medium=ads&utm_medium=?utm_campaign=Firebase_featureoverview_awareness_analytics_en_05-18-16_&utm_source=?utm_campaign=Firebase_announcement_awareness_general_en_05-18-16_&utm_source=Firebase&utm_medium=ads&utm_medium=?utm_campaign=Firebase_announcement_awareness_general_en_05-18-16_&utm_source=Firebase&utm_medium=ads) database for data storage, allowing views to be updated in realtime as they change, and providing simple interfaces for common tasks like displaying lists or collections of items.
 
 Additionally, FirebaseUI simplifies Firebase authentication by providing easy to use auth methods that integrate with common identity providers like Facebook, Twitter, and Google as well as allowing developers to use a built in headful UI for ease of development.