bug#30610: clarify linux-mode usage from Lisp

[John Shahid <jvshahid@gmail.com>]

Worth noting that this is my first patch to Emacs. Let me know if
there's anything wrong with the way I submitted the patch.

cheers,

-js

John Shahid <jvshahid@gmail.com> writes:

> From 04d261f836e5b000e8f6ed9e343417feaa8bc273 Mon Sep 17 00:00:00 2001
> From: John Shahid <jvshahid@gmail.com>
> Date: Sun, 25 Feb 2018 14:33:00 -0500
> Subject: [PATCH] clarifies linum-mode usage from Lisp
>
> ---
>  lisp/linum.el | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/lisp/linum.el b/lisp/linum.el
> index 9df0c5d023..fa66d62bfe 100644
> --- a/lisp/linum.el
> +++ b/lisp/linum.el
> @@ -76,8 +76,12 @@ linum-delay
>  (define-minor-mode linum-mode
>    "Toggle display of line numbers in the left margin (Linum mode).
>  With a prefix argument ARG, enable Linum mode if ARG is positive,
> -and disable it otherwise.  If called from Lisp, enable the mode
> -if ARG is omitted or nil.
> +and disable it otherwise.
> +
> +When called from Lisp, toggles the mode if the argument is
> +`toggle', disables the mode if the argument is a non-positive
> +integer, and enables the mode otherwise (including if the
> +argument is omitted or nil or a positive integer).
>  
>  Linum mode is a buffer-local minor mode."
>    :lighter ""                           ; for desktop.el