Add comment about threadid analysis access may_race

Author: sim642

src/analyses/threadId.ml

@@ -99,7 +99,7 @@ struct
     include Printable.Option (ThreadLifted) (struct let name = "nonunique" end)
     let name () = "thread"
     let may_race (t1: t) (t2: t) = match t1, t2 with
-      | Some t1, Some t2 when ThreadLifted.equal t1 t2 -> false
+      | Some t1, Some t2 when ThreadLifted.equal t1 t2 -> false (* only unique threads *)
       | _, _ -> true
     let should_print = Option.is_some
   end