Update SpriteMaterial.html

Add doc entry stating that SpriteMaterials are not clipped by using clippingPlanes

docs/api/materials/SpriteMaterial.html

@@ -44,6 +44,8 @@ scene.add( sprite );
 
 			The exception is the property [page:Hexadecimal color], which can be passed in as a hexadecimal
 			string and is *0xffffff* (white) by default. [page:Color.set]( color ) is called internally.
+			
+			SpriteMaterials are not clipped by using [page:Material.clippingPlanes].
 		</div>