All LiveWhale pages include the viewport meta tag by default:
<meta name="viewport" content="width=device-width, initial-scale=1"/>
If your design requires something special for that tag, though, you can set it in your public.config.php this way:
$_LW->CONFIG['VIEWPORT']='<meta name="viewport" content="width=device-width, initial-scale=1, minimum-scale=1.0"/>';