SurfaceTool add_index method exposed to scripts.

scene/resources/surface_tool.cpp

@@ -860,6 +860,7 @@ void SurfaceTool::_bind_methods() {
 	ObjectTypeDB::bind_method(_MD("deindex"),&SurfaceTool::deindex);
 	///ObjectTypeDB::bind_method(_MD("generate_flat_normals"),&SurfaceTool::generate_flat_normals);
 	ObjectTypeDB::bind_method(_MD("generate_normals"),&SurfaceTool::generate_normals);
+	ObjectTypeDB::bind_method(_MD("add_index", "index"), &SurfaceTool::add_index);
 	ObjectTypeDB::bind_method(_MD("commit:Mesh","existing:Mesh"),&SurfaceTool::commit,DEFVAL(Variant()));
 	ObjectTypeDB::bind_method(_MD("clear"),&SurfaceTool::clear);