Documentation for site.hs

[danscime]

Eventually we should have some documentation / comments in site.hs.
In the future if someone new needs to take a look and figure out how to edit the website.

From my point of view, trying to figure out how it worked took quite a bit of time, and I'm still not great with some parts of it.

[smiths]

Yes! We definitely need this kind of documentation. Since you are now an expert, I'm going to assign this issue to you. :-)

[danscime]

Documented via #1653