docs: add mcpo Docker quickstart

[Wenjunyun123]

Summary

• add a prebuilt Docker command for mcpo
• add a Docker Compose example that mounts a local config and exposes port 8000
• explain how to point Open WebUI at the mcpo proxy endpoint

Closes #627

Validation

• git diff --check HEAD~1 HEAD

[Classic298]

Thanks for this, the published-image quickstart is a nice idea. Closing for now because the examples would not work as written:

• Missing --host 0.0.0.0. mcpo binds 127.0.0.1 by default, so inside the container it listens on localhost and is unreachable through -p 8000:8000 (the proxy starts but nothing can connect). The existing "Dockerize your Proxy Server" section on this page sets --host 0.0.0.0 in its Dockerfile for exactly this reason, so the new docker run and Compose examples need it too.
• Duplicates the existing Docker section. This page already has a "🐳 Dockerize your Proxy Server using mcpo" section. Adding a second Docker block in the install step splits the Docker story in two and runs the server before step 3 ("Run the Proxy Server").

The no-build and Compose path is worth having, it's the option that section lacks. Happy to merge a revised version that adds --host 0.0.0.0 and folds these into the existing Docker section. Please feel free to reopen or open a fresh PR. Thanks for contributing!

also please avoid emojis in titles

[Wenjunyun123]

Thanks for the detailed review. I updated the branch to address both points:

• moved the no-build Docker and Compose examples into the existing Dockerize section instead of keeping a second Docker block in the install step
• added --host 0.0.0.0 to both the docker run and Compose examples so the proxy is reachable through Docker port publishing
• removed the emoji from the Docker section title

Could you please take another look and reopen this PR if the revised structure looks acceptable?