Document which files inherit and which don't in README

[JacobPEvans]

Problem

The .github README doesn't clearly document what inherits automatically vs what requires manual action.

Key Findings from ai-workflows Audit

Auto-inherited (when present at root):

• CODE_OF_CONDUCT.md, CONTRIBUTING.md, SECURITY.md, SUPPORT.md, FUNDING.yml
• Issue templates (.github/ISSUE_TEMPLATE/)
• PR templates (.github/PULL_REQUEST_TEMPLATE/)

NOT inherited (must be copied or synced):

• GitHub Actions workflows (.github/workflows/)
• Labels (requires gh label clone or label-sync automation)
• Branch protection rules
• Repository settings

Suggested Fix

Add an "Inheritance" section to the README explaining what propagates automatically and what needs manual action.

Found during ai-workflows inheritance audit.