Add CC badge to README

Author: wfleming

README.md

@@ -1,5 +1,7 @@
 # codeclimate-duplication
 
+[![Code Climate](https://codeclimate.com/github/codeclimate/codeclimate-duplication/badges/gpa.svg)](https://codeclimate.com/github/codeclimate/codeclimate-duplication)
+
 `codeclimate-duplication` is an engine that wraps [flay] and supports Ruby,
 Python, JavaScript, and PHP. You can run it on the command line using the Code
 Climate CLI or on our [hosted analysis platform][codeclimate].