It is actually quite simple just copy and paste this code into anywhere in the website and you should be all set, Positioning doesn't really matter as long as it's clickable.
<a href="https://orileytan.github.io/ad"><img border="0" src="https://orileytan.github.io/content/images/ad/ad.gif" width="88" height="31"></a>

The result should be the button bellow this text