Display Menu Description

/**
 <?php
 * Descriptions on Header Menu
 * @link https://codex.wordpress.org/Class_Reference/Walker
 *
 * @param string $item_output, HTML outputp for the menu item
 * @param object $item, menu item object
 * @param int $depth, depth in menu structure
 * @param object $args, arguments passed to wp_nav_menu()
 * @return string $item_output
 */
function sachyya_header_menu_item_desc( $item_output, $item, $depth, $args ) {

	if( 'top' == $args->theme_location && ! $depth && $item->description )
		$item_output = $item_output . '<span class="item-description">' . $item->description . '</span>';


	return $item_output;
}
add_filter( 'walker_nav_menu_start_el', 'sachyya_header_menu_item_desc', 10, 4 );