code: function isSafeToCreateProjectIn(root) {
    const validFiles = [
      '.DS_Store',
      'Thumbs.db',
      '.git',
      '.gitignore',
      '.idea',
      'README.md',
      'LICENSE',
      'web.iml',
      '.hg',
      '.hgignore',
      '.hgcheck',
    ];
    return fs.readdirSync(root).every(file => validFiles.indexOf(file) >= 0);
  }
docs: If project only contains files generated by GH, it’s safe. We also special case IJ-based products .idea because it integrates with CRA: https://github.com/facebookincubator/create-react-app/pull/368#issuecomment-243446094