Show n-install for installing n on Node.js downloads page

[shadowspawn]

Node.js has a new download page where users can get instructions on how to install Node.js in various ways:

• https://nodejs.org/en/about/previous-releases#official-versus-community
• https://nodejs.org/en/download
• https://github.com/nodejs/nodejs.org/blob/main/COLLABORATOR_GUIDE.md#the-new-downloads-page

I am thinking about adding instructions for n, and think n-install might be the most self-contained way of installing n for new users.

Some related PRs:

• feat: official vs community and instructions for downloads page nodejs/nodejs.org#7365
• docs: add Devbox as commumity download option nodejs/nodejs.org#7370

Preflight issue on n-install:

• Show n-install for installing n on Node.js downloads page? mklement0/n-install#60