docs: mention uvu-watch

[aleclarson]

I've updated uvu-watch to install filespy on-demand, so it can be used locally without slowing down CI. 🎉

Where should I mention it in docs/watch.md? Is at the top okay?

My reasoning is that yarn add uvu-watch -D && yarn test -w is the easiest way to get going. :)

[aleclarson]

Bump. The package now works with npm 6 & 7, as well as Yarn 1.

Haven't tested with Yarn 2, and pnpm does not work (but uvu core chokes on symlinks anyway).

[lukeed]

Thanks! I haven't had a time to look through yet but I will. Am planning time this week to make a big uvu pass.