Update short site name description

Signed-off-by: Matt Friedman <maf675@gmail.com>

Author: iMattPro

language/en/webpushnotifications_common_acp.php

@@ -40,7 +40,7 @@
 $lang = array_merge($lang, [
 	'PWA_SETTINGS'				=> 'Progressive web application options',
 	'PWA_SHORT_NAME'			=> 'Short site name',
-	'PWA_SHORT_NAME_EXPLAIN'	=> 'Your site name in 12 characters or less, which may be used as a label for an icon on a mobile device’s home screen.',
+	'PWA_SHORT_NAME_EXPLAIN'	=> 'Your site name in 12 characters or fewer, which may be used as a label for an icon on a mobile device’s home screen. (If this field is left empty, the first 12 characters of the <samp>Site name</samp> will be used.)',
 	'PWA_ICON_SMALL'			=> 'Small mobile device icon',
 	'PWA_ICON_SMALL_EXPLAIN'	=> 'File name of a 192px x 192px PNG image. This file must be uploaded to your board’s <samp>icons</samp> directory.',
 	'PWA_ICON_LARGE'			=> 'Large mobile device icon',