Updated documentation to include parameters for creating an instance of `MotorKit` as well noting that higher I2C frequency may be helpful for operation, if available. Thanks dhalbert!
To use in CircuitPython, simply install the [Adafruit CircuitPython Bundle](https://circuitpython.org/libraries).
To use in CPython, `pip3 install adafruit-circuitpython-motorkit`.
Read the [docs](http://circuitpython.readthedocs.io/projects/motorkit/en/latest/) for info on how to use it.