wordpress-register-sortable-column.php

<?php
/**
* instructs wordpress that our column is sortable
* @param Array - existing columns from wordpress
* @return Array - column array with new attributes
*/
function register_sortable ( $columns ) 
{
    $columns['template'] = 'template';
    return $columns;
}

add_filter('manage_edit-page_sortable_columns', 'register_sortable');