add screenshot to README

README.md

@@ -3,6 +3,8 @@
 barnard is a terminal-based client for the [Mumble](http://mumble.info) voice
 chat software.
 
+![Screenshot](https://i.imgur.com/B8ldT5k.png)
+
 ## Requirements
 
 - [gumble](https://github.com/layeh/gumble/tree/master/gumble)