1. Add script file.
Add gist embedding script into your github pages.
<script src="https://gist.github.com/Albert-W/e37d1c4fa30c430c37d7b1b1fe9b60d8.js"></script>
2. For asynchronously-loaded page
The embedding script will execute document.write function. If you are using asynchronously-loaded one error will occur. （出于浏览器的安全机制，浏览器是会禁止异步加载过来的js执行document写入操作的。）
Failed to execute 'write' on 'Document': It isn't possible to write into a document from an asynchronously-loaded external script unless it is explicitly opened.
In order to solve this problem, Iframe is required. A demo is giving as follow.