If this is a fresh install you no longer need to edit that file. Our docs in that section are slightly outdated and a new PR has been created to fix it. What you do need to do is update the paths in the site.php file to:
'base' => __DIR__,
'public' => __DIR__,
'storage' => __DIR__.'/storage',
And you need to update the $site variable in index.php to look like:
$site = require './site.php';
