In the work bowl of a food processor fitted with the metal blade, combine the cranberries, orange, sugar, and salt. Process until coarsely and evenly ground, stopping the machine once or twice to scrape down the sides of the work bowl. Add the mint, and process to combine. Transfer the relish to a serving bowl, cover, and refrigerate for several hours before serving. (The relish can be made 1 or 2 days in advance; however, wait until the day you serve it to add the fresh mint.)