index.html

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <meta http-equiv="X-UA-Compatible" content="ie=edge" />
    <title>Document</title>
    <link
      rel="stylesheet"
      href="https://cdnjs.cloudflare.com/ajax/libs/github-markdown-css/3.0.1/github-markdown.min.css"
    />
  </head>
  <body>
    <main class="markdown-body"></main>
    <script src="https://cdn.jsdelivr.net/npm/markdown-it@8.4.2/dist/markdown-it.js"></script>
    <script>
      const md = new markdownit();
      const main = document.querySelector('main');
      fetch('README.md', { cache: 'no-cache' })
        .then((res) => res.text())
        .then((text) => {
          main.innerHTML = md.render(text);
        });
    </script>
  </body>
</html>