4 ounces (½ cup) all-natural limeade, such as Newman’s Own   1 ½ ounces (1 shot) best quality Tequila, preferably Patron Silver   ½ ounce (1 tablespoon) orange-flavored liqueur, such as Cointreau or Grand Marnier   Juice from ½ lime (about a tablespoon)   Lime slices, for garnish   Coarse salt for rimming the glass