Change recommanded installation method for pnpm

[aduh95]

By the way, would be nice to have that as the recommended way to install pnpm with node.js at https://nodejs.org/en/download

Originally posted by @zkochan in nodejs/node#66101 (comment)

[bmuenzenmeyer]

Doing this would require an inversion of the dynamic form we use. Not impossible, but a huge departure from the pattern.

[aduh95]

Would adding pnpm as an alternative to nvm not be an option?

[bmuenzenmeyer]

i think that'd work, as long as we can close off the subsequent options. i need to look at how configurable it is again. If you choose pnpm like that it should just short circuit and not ask the with ... question.

Doable, just need to see how much