message: update to typo in irv3 uml model note
diff: @@ -63,7 +63,7 @@ note left of Instruction
  Ry(y)
  U(x,y,z)
  }
  - foo Composite Instruction has 2 CompositeArguments
  + foo Composite Instruction has 3 CompositeArguments
  first Rx Instruction keeps map from one with
  name x to idx == 0, second Ry keeps map of y to
  idx == 0. U keeps map {x:0, y:1, z:2}.
  