Improve/simplify TailwindCSS 'getting started' guide

[aperepel]

There's unnecessary mention of having to install node and run npx tailwind xxx in the current docs. Not required when using cargos-leptos, but needs an update to the templates and an extra config to work properly.

The build will download the proper arch pre-compiled tailwindcss cli binary and use it e.g. when running cargo leptos watch.

[aperepel]

Feel free to assign to myself, let me see if I can grab it with @aperepel