Help link doesn't appear in module page What do I have to do to show help link in module menu?

My code looks like:

/**
 * Implements hook_help().
 */
function mymodule_help($path, $arg) {
  if ($path == 'admin/help#mymodule') {
    $output = '&lt;h3&gt;' . t('About') . '&lt;/h3&gt;';
    $output .= '&lt;p&gt;' . t('descripton.') . '&lt;/p&gt;';
    return $output;
  }
}
In order to the help link appear on the module page (admin/modules), you should have both the core Help module and your module enabled.