[css-display-4] Fix syntax error

Author: fantasai

css-display-4/Overview.bs

@@ -986,8 +986,8 @@ Display Order Shorthand: the 'order' property</h3>
 	<pre class='propdef shorthand'>
 	Name: order
 	Value: [ <<'layout-order'>> <<'reading-order'>>? ] |
-	       [ reading && <<'reading-order'>> ]
-	       [ layout && <<'layout-order'>> ]
+	       [ reading && <<'reading-order'>> ] |
+	       [ layout && <<'layout-order'>> ] |
 	       [ reading-and-layout && <<integer>> ]
 	Applies to: [=flex items=] and [=grid items=]
 	Inherited: no