updated README; added Travis badge

Author: sommersoft

README.rst

@@ -10,6 +10,10 @@ Introduction
     :target: https://discord.gg/nBQh6qu
     :alt: Discord
 
+.. image:: https://travis-ci.org/adafruit/Adafruit_CircuitPython_PCA9685.svg?branch=master
+    :target: https://travis-ci.org/adafruit/Adafruit_CircuitPython_PCA9685
+    :alt: Build Status
+
 Driver for the PCA9685, a 16-channel, 12-bit PWM chip
 
 Dependencies