Fixup 'Who is Responsible for What' section

• remove 'Boot blocks' and 'Boot loader' points (these should be moved

to committers-guide IMO)

• Release Coordinator: jkh@ -> re@ headed by murray@
• Security Officer: kris@ -> security-officer@ headed by nectar@
• Ports Manager: asami@ -> portmgr@

Also add href to releng article into 'Release Coodination' point

Inspired by: docs/34656