bug#58602: 29.0.50; Please document (:documentation FORM) spec for closures

[Michael Heerdegen]

Hello,

I think we need to document this new feature described in etc/NEWS.25:

| ** Lexical closures can use '(:documentation FORM)' to build their docstring.
| It should be placed right where the docstring would be, and FORM is then
| evaluated (and should return a string) when the closure is built.

at least in the ELisp reference manual (dunno, maybe also in the
docstring of `lambda' and `defun'?).

Thanks,

Michael.