doc: improve doc on unintended breaking changes

Improve the material in the Collaborator Guide on unintended breaking
changes.

PR-URL: https://github.com/nodejs/node/pull/25887


Reviewed-By: Vse Mozhet Byt <vsemozhetbyt@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Anto Aravinth <anto.aravinth.cse@gmail.com>