Add guidance for Next.js

[haydn]

This adds a section to readme.md with some advice for people using Next.js. IMO, having a dedicated config would be a burden to maintain without adding much value (mainly because Next.js rewrites the tsconfig.json). Having some guidance should be enough to point people into the pit of success.

[mattpocock]

Thanks for the pull request! However, I think it makes more sense for frameworks themselves to own the documentation for how they work best with TypeScript.

[haydn]

@mattpocock No worries, that makes sense. 👍