Update README.rst

Add Connection Manager dep.

Author: tannewt

README.rst

@@ -25,6 +25,7 @@ Dependencies
 This driver depends on:
 
 * `Adafruit CircuitPython <https://github.com/adafruit/circuitpython>`_
+* `Adafruit CircuitPython ConnectionManager <https://github.com/adafruit/Adafruit_CircuitPython_ConnectionManager/>`_
 
 Please ensure all dependencies are available on the CircuitPython filesystem.
 This is easily achieved by downloading