Clarify release stages on "releases" page

[garybernhardt]

My team recently did our first major Node version upgrade and had a bad experience. The short version is: we tried to upgrade to Node 12 (which is in "Current" status as of today, not "Active"). We couldn't get one of our dependencies to build and ended the workday without successfully upgrading.

I'd seen the releases page multiple times, including during that attempted upgrade. However, that page doesn't explain what the various stages actually mean, and which ones are recommended for production use. Specifically, I didn't understand "Current" vs. "Active", and incorrectly assumed that either would be acceptable for production use, because neither of them was called "unstable", "testing", "alpha", "beta", "prerelease", or other terms that I'm familiar with for a "don't use this in production app yet!" release.

This change adds a paragraph with a brief explanation of the different statuses. I also included a bit about LTS, because I imagine a lot of people seeing this page won't be familiar with that term.

I think that a short explanation on the releases page will save a lot of other teams from this kind of multi-hour upgrade frustration. I've never contributed to this repo, so I may have put this text in the wrong file, and my explanation of the Node release statuses may be wrong in ways I don't understand yet. But I wanted to suggest a concrete change that would've helped us to avoid wasting half of a day.

(My understanding is based on this @jasnell tweet: https://twitter.com/jasnell/status/1128696625986015232.)

[ZainW]

This is a very nice addition to the docs, would help alot with people starting out and overall frustration when it comes to node versioning.

[fhemberger]

Please don't put content directly into the templates, we need to be able to translate all the texts. Please use locale/en/about/releases.md instead.

[Trott]

/ping @nodejs/release

[Trott]

Sorry to hear that the release info wasn't clear and caused issues for your team. Help on making that information more available and more clear is certainly appreciated.

[garybernhardt]

Thanks, @mgol, @fhemberger, and @Trott. I replaced "Node" with "Node.js", added the qualification that releases are "typically" LTS for 30 months, and moved the paragraph from the template to the localized md file. That makes it appear at the top of the page rather than the bottom, but that doesn't seem like a problem.

[fhemberger]

Thank you!

[garybernhardt]

Thanks for merging! 👍