Added Black formatting badge

Author: evaherrada

README.rst

@@ -13,6 +13,10 @@ Introduction
  :target: https://github.com/adafruit/Adafruit_CircuitPython_ST7789/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
+
 displayio driver for ST7789 TFT-LCD displays.
 
 Dependencies