docs: add docker-compose example to README

[gordonmurray]

Summary

Adds a Docker Compose snippet to the README showing how to run lance-data-viewer alongside other services with a shared data volume.

• Uses a named volume mounted read-only
• Maps to port 8888 on the host to highlight that 8080 can conflict with Airflow, Jenkins, etc.
• Placed between Configuration and Images sections

Fixes #26

Test plan

• Verify the YAML snippet is valid (docker compose config)
• Confirm it renders correctly on GitHub