Add release badge

Author: garyb

README.md

@@ -1,5 +1,6 @@
 # purescript-dom
 
+[![Latest release](http://img.shields.io/bower/v/purescript-dom.svg)](https://github.com/purescript-contrib/purescript-dom/releases)
 [![Build Status](https://travis-ci.org/purescript-contrib/purescript-dom.svg?branch=master)](https://travis-ci.org/purescript-contrib/purescript-dom)
 [![Maintainer: garyb](https://img.shields.io/badge/maintainer-garyb-lightgrey.svg)](http://github.com/garyb)