Whereas previously, I'd had everything as an `<h2>` as I thought it
looked more semantic (due to the post's title being a `<h1>`, it seems
like Hugo doesn't do that - and it makes sense as to why not now.

Therefore we need to un-indent everything a little bit, replacing `<h2>`
with `<h1>` and so on.

This then means that our TOC then looks much nicer, when it's shown.