Add codecov badge

Author: maxnz

README.md

@@ -2,6 +2,7 @@
 
 [![Build Status](https://travis-ci.com/AnimatedLEDStrip/client-python.svg?branch=master)](https://travis-ci.com/AnimatedLEDStrip/client-python)
 [![PyPI](https://img.shields.io/pypi/v/animatedledstrip-client.svg)](https://pypi.python.org/pypi/animatedledstrip-client)
+[![codecov](https://codecov.io/gh/AnimatedLEDStrip/client-python/branch/master/graph/badge.svg)](https://codecov.io/gh/AnimatedLEDStrip/client-python)
 
 This library allows a Python 3 client to connect to an AnimatedLEDStrip server, allowing the client to send animations to the server and receive currently running animations from the server, among other information.