Added Coveralls badge to README.md

Author: hluk

README.md

@@ -2,6 +2,7 @@ CopyQ
 =====
 
 [![Build Status](https://travis-ci.org/hluk/CopyQ.png)](https://travis-ci.org/hluk/CopyQ)
+[![Coverage Status](https://coveralls.io/repos/hluk/CopyQ/badge.png?branch=master)](https://coveralls.io/r/hluk/CopyQ?branch=master)
 [![Stories in Ready](https://badge.waffle.io/hluk/CopyQ.png)](http://waffle.io/hluk/CopyQ)
 
 CopyQ is clipboard manager with searchable and editable history.