How can I tie the Display Face Orientation to a Toggleable hotkey? I already have the... thing: 


  bpy.context.space_data.overlay.show_face_orientation


This accepts a boolean value. I found this out by looking at the Info menu. 

I think it's called a context attribute?

I just don't know how to set its value to True or False with a toggleable hotkey.
In 2.8x, it's simpler than that. Just open the overlays panel, right-click the Face Orientation check-box, and select 'Assign Shortcut' from the menu.