Add 'swimmingpool' unit

modules/units/misc.nbt

@@ -53,6 +53,9 @@ unit molal: Molality = 1 mole / kilogram
 # Standard FIFA football pitch
 unit footballfield: Area = 105 m × 68 m
 
+# Olympic-size swimming pool (FR3)
+unit swimmingpool: Volume = 50 m × 25 m × 2 m
+
 # Angles
 
 @aliases(turns)