Refs taskrabbit#36, update README.md to show screenshots

Author: jeffreyleeon

README.md

@@ -4,6 +4,11 @@ At [TaskRabbit](https://www.taskrabbit.com), we are trying to understand the bes
 
 The app itself is vaguely like twitter/tumblr. There are users that make posts. They follow other users. You can look at follows and their posts. The features (or styling) isn't the main point. At this time, we're mostly demonstrating architectural concepts.
 
+![Sign up](./screenshots/sign_up.png "Sign up")
+![Create post](./screenshots/create_post.png "Create post")
+![Show post](./screenshots/show_post.png "Show post")
+![Followers](./screenshots/follows.png "Followers")
+
 ### iOS
 In the root directory
 * Install dependencies: `npm install`