add example to docs

docs/api/en/core/Layers.html

@@ -21,6 +21,11 @@
 			All classes that inherit from [page:Object3D] have an [page:Object3D.layers] property which is an instance of this class.
 		</p>
 
+		<h2>Examples</h2>
+
+		<p>
+			[example:webgl_layers WebGL / layers]
+		</p>
 
 		<h2>Constructor</h2>