Docs: Update Object3D to reflect new semantics for .renderOrder

docs/api/en/core/Object3D.html

@@ -124,7 +124,8 @@
 		<h3>[property:Number renderOrder]</h3>
 		<p>
 		This value allows the default rendering order of [link:https://en.wikipedia.org/wiki/Scene_graph scene graph]
-		objects to be overridden although opaque and transparent objects remain sorted independently.
+		objects to be overridden although opaque and transparent objects remain sorted independently. When this property
+		is set for an instance of [page:Group Group], all descendants objects will be sorted and rendered together.
 		Sorting is from lowest to highest renderOrder. Default value is *0*.
 		</p>