Document clippingPlanes render setting dependency

docs/api/materials/Material.html

@@ -85,6 +85,7 @@
 		User-defined clipping planes specified as THREE.Plane objects in world space.
 		These planes apply to the objects this material is attached to.
 		Points in space whose signed distance to the plane is negative are clipped (not rendered).
+		This requires [page:WebGLRenderer.localClippingEnabled] to be *true*.
 		See the [example:webgl_clipping_intersection WebGL / clipping /intersection] example.
 		Default is *null*.
 		</div>