https://drupalsun.com/eelke/2018/08/24/quick-tip-generating-hash-salt-drupal-8
Use this to generator a salt hash so that its not included in your settings.php file if you commit that file to your repo.
drush php-eval 'echo \Drupal\Component\Utility\Crypt::randomBytesBase64(55)' > salt.txt
// alternative
drush php-eval 'echo \Drupal\Component\Utility\Crypt::randomBytesBase64(55)' > drupal\salt.txt