The game should be able to switch over to a gamepad automatically when you connect it. If that isn't working then I'd suggest Joy2Key as a temporary solution. What kind of joystick are you using?
After posting this post, I did try with a Razer Wolverine Ultimate , and it now works. However, it doesn't work with Mayflash Arcade F300 Elite or with my MadCatz SF V TE2. Later on, I will give it a try with the Joy2Key.
I got my Mayflash F300 (non-elite) to work by switching to Xinput instead of Dinput. I haven't had much luck getting Dinput pads to work with the game so far.
