That addresses the issue of putting a derailleur on the frame. But keep in mind that true track frames are seldom drilled for mounting brakes, so you'll need to deal with that as well. Depending on what drill equipment you have available, you may end up needing to use nutted, rather than recessed Allen head fittings. And track frames tend to be pretty close-coupled, meaning brake reach may be an issue. Before you get out the drill, make sure you'll be able to find calipers that will fit the frame so the pads properly reach the brake track on the rim. Ultimately, as others have pointed out, you may find it more cost-effective to simply buy a used road bike instead.