Add super-simple site structure

[sarahmonster]

This will both show how to use CSS in a site, and also avoid this super ugly thing:

Just some sort of max-width on the main content area should do the trick.

[tofumatt]

Yeah, that's fair. I did nothing with the base content, but some simple skeleton would be good 👍

[sarahmonster]

A lot of starter themes don't bother, but that's always sort of driven me bananas and it means it's always the first thing I do when starting up a new site. Giving a bit of a baseline structure makes it a little bit easier to get up and running with something, and it's easy enough to remove. See #32 for a suggested approach!

[tofumatt]

Especially as we're building this for us first, I agree. Some kind of starter is great.