Added Black formatting badge

Author: evaherrada

README.rst

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     :alt: Build Status
 
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 This library will allow you to control the LEDs and read button presses on the `Adafruit Trellis
 Board <https://www.adafruit.com/product/1616>`_. It will work with a single Trellis board, or
 with a matrix of up to 8 Trellis boards.