doc: expand on squashing and rebasing to land a PR
Document the choice of squashing and rebasing when landing a pull request containing more than one subsystem commits.
Refs: https://github.com/nodejs/node/pull/47956#issuecomment-1631783652
Do not update/delete: Banner broadcast message test data
Do not update/delete: Notification broadcast message test data
Document the choice of squashing and rebasing when landing a pull request containing more than one subsystem commits.
Refs: https://github.com/nodejs/node/pull/47956#issuecomment-1631783652