Install instructions missing a step for tailwindcss

[dewey]

Issue with Reference
On https://getkirby.com/docs/cookbook/frontend/kirby-meets-tailwindcss#install-tailwind-css the instructions only say to install npm install tailwindcss@latest. This will not be enough as then the npm run watch command later will fail as we didn't install the cli tooling.

npm error could not determine executable to run

Expected
We also need to install npm install tailwindcss @tailwindcss/cli, then it'll work.