code: function checkRequiredFiles() {
    const indexHtmlExists = fse.existsSync(paths.indexHtml);
    const indexJsExists = fse.existsSync(paths.indexJs);
  
    if (!indexHtmlExists || !indexJsExists) {
      logError('\nSome required files couldn\'t be found. Make sure these all exist:\n');
      logError(`\t- ${paths.indexHtml}`);
      logError(`\t- ${paths.indexJs}\n`);
  
      process.exit(1);
    }
  }
docs: Warn and crash if required files are missing.