Update README.md

Author: thijse

README.md

@@ -1,6 +1,7 @@
 ArduinoLog - C++ Log library for Arduino devices
 ====================
 [![Build Status](https://travis-ci.org/thijse/Arduino-Log.svg?branch=master)](https://travis-ci.org/thijse/Arduino-Log)
+[![License](http://img.shields.io/:license-mit-blue.svg)](http://doge.mit-license.org)
 
 *An minimalistic Logging framework  for Arduino-compatible embedded systems.*