[dzianisv]

Summary

Clarify what dzianisv/codex carries on top of openai/codex so the README explains when to use the fork versus upstream.

Closes #50.

Changes

• rename the old fork feature section into an explicit upstream-comparison section
• document the fork's runtime /model work, provider-catalog integration, Copilot compatibility fixes, reflection support, and fork-specific CI/release maintenance patches
• add maintenance notes describing how the fork should stay narrow and continue tracking upstream

Testing

• reviewed the rendered markdown diff locally