clarify rayon-futures README
@@ -227,7 +227,7 @@ This is good, because there *are* still active refs to the
sources of these: unpark values and the future result.
**NotifyHandle values.** We may have given away `NotifyHandle` values --
-these are trait objects, but they are actually refs to our
+these contain trait objects that are actually refs to our
`ScopeFuture`. Note that `NotifyHandle: 'static`, so these could be
floating about for any length of time (we had to transmute away the
lifetimes to give them out). This is ok because (a) the `Arc` keeps
