Set deprecation note on llm-d-routing sidecar

[elevran]

Sidecar code has been moved to inference-scheduler as part of #379.
This should be clearly marked on the original repo in its README.
In addition, any pending sidecar PR's and issues, should be moved to inference-scheduler repo.

[elevran]

Fixed by llm-d/llm-d-routing-sidecar#66