Soak the mung beans in 2 c water for 20 minutes. Drain & place in a large pot. Add 10 c water & cook over medium heat, uncovered, for 15 minutes. Dissolve the arrowroot in quarter c hot water & stir into the mung beans. Add the sugar & cook, stirring, for 15 minutes, or until all the water has been absorbed. Remove from the heat. In a small pot, heat the coconut milk with the salt for 5 to 7 minutes or until it begins to boil. Serve the pudding in individual bowls, topped with 1 tb coconut milk. It will keep in the refrigerator for 1 week & may be served either hot or cold.