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_INA219.svg?branch=master
+    :target: https://travis-ci.org/adafruit/Adafruit_CircuitPython_INA219
+    :alt: Build Status
+
 CircuitPython driver for the `INA219 current sensor <https://www.adafruit.com/product/904>`_.
 
 Dependencies