Hello and welcome to the forums [member=soltic].
Probably the best way is to modify the example.php file under application/views and separate it to logical views, e.g.
head.php, header.php,menu.php,content.php,footer.php
and then witihn your output function call these views,
$this->load->view('head', $data_head);
$this->load->view('header', $data_header);
$this->load->view('menu', $data_menu);
$this->load->view('content', $data_content); // this could be the output from $this->grocery_crud->render();
$this->load->view('footer', $data_footer);
UPDATE: Of course you need to know how to pass some data from the output of the Grocery CRUD's render function because it contains the js and css files.
Just see the index() controller function of the example.php and you will know what to do.