how to add a favicon

Hi! Great theme! just trying to add a favicon but can’t seem to get it to work. other themes seem to have a customizer spot to do it easily but not this one. so i tried to add simple code with no luck (placed it in the header section using the editor)
***this line included for location reference***<link rel=”pingback” href=”<?php bloginfo( ‘pingback_url’ ); ?>”>
<link rel=”shortcut icon” href=”<?php echo get_stylesheet_directory_uri(); ?>/TLfavicon01.png” />
***
(also tried to add the file as a .ico but it kept converting back to .png so i changed the code to reflect .png)
any help would be appreciated! thanks, Marc
site is http://www.twistlift.com