bug#63875: 26.3; Doc of `dired-guess-shell-alist-user'

[Eli Zaretskii]

> From: Drew Adams <drew.adams@oracle.com>
> CC: "63875@debbugs.gnu.org" <63875@debbugs.gnu.org>
> Date: Sat, 3 Jun 2023 16:26:02 +0000
> 
> > Feel free to close the bug.  Thx.
> 
> But it would be good, I think, to add that it's
> not just about shell commands.  Some users will
> not recognize that they can invoke executable
> programs this way.

Shell commands are a super-set of executable programs, so I see no
reason to change anything here.  The variable is used to invoke
commands via a shell, so "shell command" is exactly right.