Editing 404 page on Github pages

By default Octopress doesn't include a 404 page, so on GitHub it's shown as follows:

Usually, with a Rack server you need to modify the config.ru file to handle exceptions (this website explains this case), but in my case I can't manage the server side, so GitHub gives us another way: they use a 404.html file as the default 404 page, as you can read on their documentation.

In summary, you need to create a new file at the path sources/404.html and it will be used as 404. You can see what mine looks like in 404.html, and this is the code:

---
layout: default
---
<h1 style="text-align: center">Page not found</h1>
<p style="text-align:center">You can find other posts on <a href="/archives">Archives</a> of this blog, or directly go to <a href="/">the main page</a></p>
<img src="/images/404.png" style="max-width: 100%; margin: 0 auto; display: block" />
<small style="display:block; float:right">Credits of the image: <a href="http://refinedmobile.com/404">refinedmobile.com</a></small>