Meta: documentation request v3 vs v2

[samv]

Spring v3 functions look great! However it looks like current (non v3) versions of Helm are pinned to Sprig v2. Some kind of note that the documentation is for v3 and not v2 would be useful. Having v2 documentation also available online would be nice, too. And I would also recommend a practice of having "introduced in version" notes on new functions going forward, or perhaps an outlink to a Changelog file or something where such user-facing changes are described. Thanks for writing Sprig!

[mattfarina]

That's a great idea. PRs welcome