Add TestFlight link to README (#2194)

* Add TestFlight link to README

* Update README.md

Author: rnystrom

README.md

@@ -1,7 +1,16 @@
 <a href="https://itunes.apple.com/app/githawk-for-github/id1252320249"><img src="Design/githawk-pulse.gif" /></a>
 <p align="center"><a href="https://itunes.apple.com/app/githawk-for-github/id1252320249"><img src="Design/app-store-badge.png" width="250" /></a></p>
 
-[![Build Status](https://www.bitrise.io/app/a912ff037bca7072/status.svg?token=PMpBs9u-C7CBIKPwNLSJrg&branch=master)](https://www.bitrise.io/app/a912ff037bca7072)
+<p align="center">
+    <a href="https://www.bitrise.io/app/a912ff037bca7072">
+        <img src="https://app.bitrise.io/app/a912ff037bca7072/status.svg?token=PMpBs9u-C7CBIKPwNLSJrg&branch=master"
+             alt="Build Status">
+    </a>
+    <a href="https://testflight.apple.com/join/QIVXLkkn">
+      <img src="https://img.shields.io/badge/Join-TestFlight-blue.svg"
+           alt="Join TestFlight" />
+    </a>
+</p>
 
 GitHawk is the highest rated iOS app for GitHub.
 
@@ -26,8 +35,6 @@ We are always looking for contributions from **all skill levels**! A great way t
 - 👩‍💻 **iOS Project Management**
   - There is a _lot_ of low-hanging fruit with our project setup, test and deployment automation, build optimizations, and more! I (@rnystrom) have no idea what I'm doing here. Come point us in the right direction!
 
-If you would like to test the latest changes, join the **TestFlight** beta by DMing your e-mail address to [@_ryannystrom](https://twitter.com/_ryannystrom).
-
 ## Installation
 
 If you want to build GitHawk locally, run `npm install`.