Do you have tabs on the fork and the frame? From the pictures on the Kona site, it looks like you don't.
If you want to run a front disc brake, you could get a Kona Project 2 disc fork, swap the front hub or just replace the entire wheel, and get something like an Avid BB7 (rotor, caliper, pads, hardware).
For the rear, you can get some adapters to mount the caliper setup but I don't know anything about those. And again, you'll have to swap the wheel or get a new hub and get the rear disc brake.
So basically, not a quick and simple or really cheap task.