Add meta descriptions for each page

[MrGreenTea]

See some info here: https://developer.chrome.com/docs/lighthouse/seo/meta-description

Should probably add a description prop to our Layout component.

[MrGreenTea]

I've added a first draft on a branch, see linked commit.
I was unsure if every page should have a description, but I think so. Chromes Lighthouse test recommends it for better SEO.