feat(templates/install): warning for distro package managers

[lambda-fairy]

It's implied by the rest of the docs, but I think it's worth making it explicit, given how often the problem appears on Zulip.

[kbuzzard]

Maybe you should add that at the time of writing lean 4 is making new releases every few weeks, so it's highly likely that the version in your package manager is already out of date?

[lambda-fairy]

Thanks @kbuzzard, added.

Also added a note about elan handling multiple versions. (I hedged my point with "most" to placate the Nix fans)

[PatrickMassot]

I don't understand the placement of those paragraph, and I don't understand the last sentence.

And I'm skeptical about the general idea. People who arrive at those web page already decided they were not using their package managers.

[jcommelin]

I agree with Patrick that I don't understand the last sentence.

Otoh, I don't think it hurts to add this warning: I often skim install pages in combination with installation via distro package managers.

[PatrickMassot]

I am closing this since it did not converge.