(Defining Minor Modes): Explain effect of command

defined with define-global-minor-mode on new buffers.

lispref/modes.texi

@@ -1480,12 +1480,15 @@ See the command \\[hungry-electric-delete]."
 @end smallexample
 
 @defmac define-global-minor-mode global-mode mode turn-on keyword-args@dots{}
-This defines a global minor mode named @var{global-mode} whose meaning
-is to enable the buffer-local minor mode @var{mode} in every buffer.
-To turn on the minor mode in a buffer, it uses the function
+This defines a global toggle named @var{global-mode} whose meaning is
+to enable or disable the buffer-local minor mode @var{mode} in all
+buffers.  To turn on the minor mode in a buffer, it uses the function
 @var{turn-on}; to turn off the minor mode, it calls @code{mode} with
 @minus{}1 as argument.
 
+Globally enabling the mode also affects buffers subsequently created
+by visiting files, but not buffers subsequently created in other ways.
+
 Use @code{:group @var{group}} in @var{keyword-args} to specify the
 custom group for the mode variable of the global minor mode.
 @end defmac