docs: function _main() {
    const contributors = JSON.parse(readFileSync(CONTRIBUTORS_PATH, 'utf8'));
    const expectedImages = Object.keys(contributors)
        .filter(key => !!contributors[key].picture)
        .map(key => join(IMAGES_DIR, contributors[key].picture));
    const missingImages = expectedImages.filter(path => !existsSync(path));
  
    if (missingImages.length > 0) {
      throw new Error(
          'The following pictures are referenced in \'contributors.json\' but do not exist:' +
          missingImages.map(path => `\n  - ${path}`).join(''));
    }
  }