* lisp/emacs-lisp/generator.el (iter-defun): Add 'doc-string' prop.

lisp/emacs-lisp/generator.el

@@ -681,7 +681,8 @@ When called as a function, NAME returns an iterator value that
 encapsulates the state of a computation that produces a sequence
 of values.  Callers can retrieve each value using `iter-next'."
   (declare (indent defun)
-           (debug (&define name lambda-list lambda-doc def-body)))
+           (debug (&define name lambda-list lambda-doc def-body))
+           (doc-string 3))
   (cl-assert lexical-binding)
   (let* ((parsed-body (macroexp-parse-body body))
          (declarations (car parsed-body))