Added Black formatting badge

Author: evaherrada

README.rst

@@ -15,6 +15,10 @@ Introduction
     :target: https://github.com/adafruit/Adafruit_CircuitPython_DHT/actions
     :alt: Build Status
 
+.. image:: https://img.shields.io/badge/code%20style-black-000000.svg
+    :target: https://github.com/psf/black
+    :alt: Code Style: Black
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 CircuitPython support for the DHT11 and DHT22 temperature and humidity devices.
 
 Dependencies