Hey John!
I usually map NES controls to a keyboard like this:
Arrow Keys = Dpad (up, down, left, right)
Z/X = A and B
Return = Start
R Shift = Select
Mobile controls and gamepad support is not necessary.
I do not expect developers to include these features as it would be extra development time, but you can always go the extra mile and make your game mobile friendly if you'd like to.