Add screenshot to readme

README.md

@@ -9,6 +9,8 @@ Mastodon
 
 Mastodon is a federated microblogging engine. An alternative implementation of the GNU social project. Based on ActivityStreams, Webfinger, PubsubHubbub and Salmon.
 
+![Screenshot](https://i.imgur.com/hzWZdYT.png)
+
 Focus of the project on a clean REST API and a good user interface. Ruby on Rails is used for the back-end, while React.js and Redux are used for the dynamic front-end. A static front-end for public resources (profiles and statuses) is also provided.
 
 If you would like, you can [support the development of this project on Patreon][patreon]. Alternatively, you can donate to this BTC address: `17j2g7vpgHhLuXhN4bueZFCvdxxieyRVWd`