Update CONTRIBUTING.md
Changes proposed in this pull request:
- Replace existing (or missing) CONTRIBUTING.md with the organisation-standard version.
- Ensure every repository reflects the current Cloud.gov contribution policy.
- Commit is cryptographically signed (Verified).
Things to check
- Could any log line expose sensitive data?
- Is a logging level below INFO suppressing debug chatter?
Security considerations
Documentation-only; introduces no executable code and no new attack surface.