It says

cp /app/code/sample-public-front-page.txt /app/data/index.php
# now fix the require_once path in /app/data/index.php from dirname(__FILE__).'/includes/load-yourls.php' to '/app/code/includes/load-yourls.php'

The second instruction is not enough -- replacing the path is not enough. That alone doesn't work, you end up with a blank page. I used your resolution and it works fine for me as well now:

- require_once( dirname(__FILE__).'/app/code/includes/load-yourls.php' );
+ require_once( '/app/code/includes/load-yourls.php' );