doc: revise N-API versions matrix text

Revise text for clarity, brevity, and conformance with our style guide.

PR-URL: https://github.com/nodejs/node/pull/34566


Reviewed-By: Gus Caplan <me@gus.host>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: James M Snell <jasnell@gmail.com>