Tape the area! Make sure that the tape is pressed down firmly! Otherwise you might have some leakage, which is a pain in the you know what to fix!
Paint a few coats:
Wait a few days for the paint to cure. Then rub chalk all over the painted area.
And then you are set! I thought this might be good for writing list's on or cute notes for the kids! You'll have to excuse my handwriting. It never quite advanced beyond the second grade!