doc: encourage 2FA before onboarding
Checklist
-
documentation is changed or added -
commit message follows commit guidelines
Affected core subsystem(s)
doc
Description of change
In the onboarding document, add a note to ask the new Collaborator if they are using two-factor authentication on their GitHub account. If they are not, suggest that they enable it as their account will have elevated privileges in mamy of the Node.js repositories.