bug#30389: 26.0.91; url-handler-mode needs to be documented

[Andy Moreton]

On Wed 15 May 2019, Lars Ingebrigtsen wrote:

> Michael Albinus <michael.albinus@gmx.de> writes:
>
>> url-handler-mode is not documented in any manual shipped with
>> Emacs. This shall be done.
>
> The doc string isn't very helpful either.  I have no idea what it's
> trying to say here.  :-)
>
> ---
>
> Toggle using `url' library for URL filenames (URL Handler mode).

The doc is indeed not very helpful. The code shows it is toggling
support for file handlers which allow URLs to the treated as filenames:

(file-exists-p "https://www.gnu.org/";)
=> nil
(url-handler-mode)
=> t
(file-exists-p "https://www.gnu.org/";)
=> t