doc: update README to make Node.js description clearer

Fixes: https://github.com/nodejs/node/issues/24872

PR-URL: https://github.com/nodejs/node/pull/31266


Reviewed-By: David Carlier <devnexen@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Rich Trott <rtrott@gmail.com>