Suggest to include a not about need for [knob] external from flatgui

[shakfu]

Hi,

Great abstraction for the apc40. Pretty much exactly what I was looking for. Thanks!

May I suggest, however, to include a note, in the README, about the need to include a [knob] object/external from the flatgui library using deken if one is running vanilla pd.

[musicus]

There are many knobs available. I do like the [knob], or [mknob], or [abcknob].