function createReadmePage(pluginDir, isLocal) {
  const packageJson = require(resolveApp(`plugins/${pluginDir}/package.json`));
  const initialContents = fs
    .readFileSync(`./plugins/${pluginDir}/README.md`)
    .toString();

  const converter = new showdown.Converter();
  converter.setFlavor('github');
  // By default, showdown preserves line breaks from the README file that are
  // just there to stay under 80 characters per line. Turn that off.
  converter.setOption('simpleLineBreaks', false);
  converter.setOption('ghMentions', false);
  const text = initialContents;
  const html = converter.makeHtml(text);

  const initialPage = `<!DOCTYPE html>
  <head>
    <title></title>
  </head>
  <body class="root">
    <article class="article-container site-width">
      <div class="article">
      ${html}
      </div>
    </article>
  </body>
 </html>
  `;

  // Add the same header, nav bar, and footer as we used for the playground.
  let modifiedContents = injectHeader(
    initialPage,
    `${packageJson.name} Demo`,
    isLocal,
  );
  modifiedContents = injectPluginNavBar(
    modifiedContents,
    packageJson,
    pluginDir,
    isLocal,
  );
  modifiedContents = injectFooter(modifiedContents);

  // Make sure the directory exists, then write to it.
  const dirString = `./gh-pages/plugins/${pluginDir}/`;
  fs.mkdirSync(dirString, {recursive: true});
  fs.writeFileSync(`${dirString}/README.html`, modifiedContents, 'utf-8');
}
Create the README page (in HTML) from the plugin's README.md file.
This includes the same header, nav bar, and footer as the playground page
for a given package.
@param {string} pluginDir The directory of the plugin that is currently
    being prepared.
@param {boolean} isLocal True if building for a local test. False if
    building for gh-pages.