In 6f8a944, titled

  Change return type of unstable `Waker::noop()` from `Waker` to `&Waker`.

the summary line for Waker was changed:

  -    /// Creates a new `Waker` that does nothing when `wake` is called.
  +    /// Returns a reference to a `Waker` that does nothing when used.

and the sentence about clone was added.

LocalWaker's docs were not changed, even though the types were, but
there is no explanation for why not.  It seems like it was simply a
slip induced by the clone-and-hack.

Based on a suggestion from @kpreid, with some further editing.