Clean the area, apply a good antibiotic ointment such as a plain triple antibiotic ointment and then wrap it. While it doesn't look too bad, this is a wound that you need to keep an eye on because it could have damaged the tendon or tendon sheath and infections in these structures can be very serious.
Call your vet and see if he ok's the use of a bit of Bute to help with the swelling and to get his list of things to watch for that would indicate a need for more serious evaluation and treatment.