[contributor-docs] Add guidance for Node version support in projects

We should make sure that the company is on the same page about how Node versions ought to be specified in projects and which versions of Node we ought to support.

* What version(s) of Node.js should be run in a development, CI, or production environment? Evaluate risk of running EOL Node.js versions in these environments.
* For OSS projects, should the minimum supported Node.js version track the above? When _can_ OSS projects drop an old version of Node.js, when _should_ they, and when _must_ they?
* Any special considerations for odd-numbered releases? These versions do not enter LTS and have a lifespan of about nine months.
* Given Node.js has a [documented release cadence|https://github.com/nodejs/release] — a version going EOL should not be a surprise — how should projects use this info to _stay_ within the guidelines over time?

No file, test, or entry point is named. Start by reviewing the linked Node.js release cadence and research the risks of EOL versions. Done means contributor guidance covers development, CI, production, OSS minimum versions, odd-numbered releases, and how projects should stay current over time.

Written by the indexing model from the issue text.