Update README.rst

Add missing lib in Dependencies section.

Author: nvtkaszpir

README.rst

@@ -22,6 +22,7 @@ This driver depends on:
 
 * `Adafruit CircuitPython <https://github.com/adafruit/circuitpython>`_
 * `Bus Device <https://github.com/adafruit/Adafruit_CircuitPython_BusDevice>`_
+* `Register <https://github.com/adafruit/Adafruit_CircuitPython_Register>`_
 
 Please ensure all dependencies are available on the CircuitPython filesystem.
 This is easily achieved by downloading