Added Black formatting badge

Author: evaherrada

README.rst

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     :target: https://github.com/adafruit/Adafruit_CircuitPython_AVRprog/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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 Program your favorite AVR chips directly from CircuitPython with this handy helper class that will let you make stand-alone programmers right from your REPL. Should work with any/all AVR chips, via SPI programming. Tested with ATmega328, ATtiny85 and ATmega2560
 
 Dependencies