Add stronger recommendations to README on support level

[leerob]

• What versions of Nuxt are supported with this builder
• How should I move to Nuxt 3 + zero config builder with Nitro?
• Should this repository be archived? Will more updates or patches be made here?

It would then be great to reflect some of that state on the v2 docs – we have seen customers be confused if they need the builder or not, when I believe we want to continue recommending using v2 and the zero-config setup.

[danielroe]

Thoughts welcome on the latest docs update. 🙏

We plan to continue bug fixes with this builder until Nuxt 2 reaches End of Life (at the end of 2023), but we would urge people to migrate to the latest version of Nuxt.