add screenshot to readme

README.md

@@ -1,10 +1,10 @@
 Kanboard Plugin Coverimage
 ==========================
 
-![Min Knaboard Version](https://img.shields.io/badge/min.%20Kanboard%20version-1.0.27-green.svg)
-
 This plugin adds a coverimage function to the board.
 
+![cover_screenshot](https://cloud.githubusercontent.com/assets/1961634/23507319/c7e38892-ff4c-11e6-90c5-453f9bda4a0f.png)
+
 Plugin for https://github.com/fguillot/kanboard
 
 Author