[Feature]: Document /occode-sync in openclawcode README

[zhyongrui]

Summary
Add a short operator-facing note in docs/openclawcode/README.md that mentions the /occode-sync chat command.

Problem to solve
The plugin integration doc already describes /occode-sync, but the product README under docs/openclawcode/ does not mention that operators can force a reconciliation pass from chat. That makes the recovery path harder to discover.

Proposed solution
Update docs/openclawcode/README.md with a short section or bullet that explains:

• /occode-sync exists
• it reconciles local run records and tracked GitHub PR status
• it is intended as a manual operator recovery command

Impact
Affected users/systems/channels
Operators validating the bundled OpenClaw chat adapter in this repository.

Severity
Low, but it slows down manual validation and troubleshooting.

Frequency
Whenever someone tries to understand the current chatops recovery surface from docs only.

Consequence
Extra manual digging through deeper integration docs before testing or operating the plugin.