bug#57937: 29.0.50; Improve doc of (interactive current-prefix-arg ...)

[Stefan Kangas]

Eli Zaretskii <eliz@gnu.org> writes:

> There is already such a pointer there:
>
>    There are three possibilities for the argument ARG-DESCRIPTOR:
>
>    • It may be omitted or ‘nil’; ...
>    • It may be a string; ...

I was thinking of this item:

   • It may be a Lisp expression that is not a string; ...

Here, I'd like to see an example like:

          (interactive current-prefix-arg)

and a brief pointer to `(elisp) Prefix Command Arguments'.