Update README.md

Added Coverage status badge

Author: keilw

README.md

@@ -14,5 +14,5 @@ http://javamoney.java.net
 
 [![Maven Central](https://maven-badges.herokuapp.com/maven-central/javax.money/money-api/badge.svg)](https://maven-badges.herokuapp.com/maven-central/javax.money/money-api)
 [![Build Status](https://api.travis-ci.org/JavaMoney/jsr354-api.png?branch=master)](https://travis-ci.org/JavaMoney/jsr354-api)
-
+[![Coverage Status](https://coveralls.io/repos/JavaMoney/jsr354-api/badge.svg?branch=master)](https://coveralls.io/r/JavaMoney/jsr354-api?branch=master)
 [![Built with Maven](http://maven.apache.org/images/logos/maven-feather.png)](http://maven.org/)