Issue #3228531 by joachim: document run-tests.sh as not intended for public consumption

/**

 * @file

 * This script runs Drupal tests from command line.

 * Script for running tests on DrupalCI.

 *

 * This script is intended for use only by drupal.org's testing. In general,

 * tests should be run directly with phpunit.

 *

 * @internal

 */

use Drupal\Component\FileSystem\FileSystem;