Footer icons Font Awesome not working properly

[ewuerger]

Hi and thank you for this awesome theme,

I've set up a GitHub footer icon from Font Awesome by following the documentation, but it just wouldn't display. From the Font Awesome website it displays this code snippet:

<i class="fa-brands fa-github"></i>

After adding the missing fa-brands class it was working. This may also fix #400 and I suggest to update the docs section.

[umarcor]

Done in #629.