Hi there, Alex!
First off, great job finding and trying that tutorial. That’s exactly the right place and will get you what you’re looking for.
If you’re getting a PHP error, then it’s likely that the there is either a typo in your snippet or the snippet is in an incorrect place in the functions.php file.
Here’s the snippet you will want to use:
https://gist.github.com/geoffgraham/35be50c46146a55e7855
I tested it out and it seems to do the trick. You’ll just want to make sure it is properly placed in your functions.php file. Typically, that’s at the very end of the file, though that can vary based on your theme or other customizations that have been made. 🙂
Cheers!
Geoff