Link to internal homepage:
<div id="custom-link">designed and edited by <a href="<?php echo esc_url( home_url( '/' ) ); ?>" rel="home">CLICK TEXT HERE</a></div>
Link to external site:
<div id="custom-link">designed and edited by <a href="EXTERNAL LINK HERE" rel="home">CLICK TEXT HERE</a></div>
Place just above closing </footer> tag.