[Docs] Update Docker deployment documentation

[pi314ever]

The default config for spawning with docker does not work OOTB. Here are the issues:

1. URL needs to be https://localhost or https://127.0.0.1
2. Docker image uses local opencode:latest instead of official ghcr.io/anomalyco/opencode:latest
3. Docker command repeats opencode command instead of just appending serve --port 4096 --hostname '0.0.0.0' to docker image, which causes docker container to exit immediately after printing help

[sudo-tee]

Thanks for the report

If you have a working setup. Can you post a PR updating the README. I personally don't use a docker set-up for opencode so I would write them blindly.

Thanks a lot