docs docker.md: example to use bind mounts

[odie5533]

Summary

Update the extended docker example to use bind mounts and avoid creating extra layers and avoid copying files into layers

This is in line with the official Docker templates for Python applications (you can try them out using docker init. I found them very helpful!)

[charliermarsh]

Thank you! Tagging @zanieb for review.

[zanieb]

If you're interested, this could be changed over in https://github.com/astral-sh/uv-docker-example/blob/main/Dockerfile too!

[konstin]

How does this interact with caching, will uv sync --frozen --no-install-project rerun when uv.lock changed? https://docs.docker.com/engine/storage/bind-mounts/ doesn't talk about caching and https://docs.docker.com/build/cache/ doesn't say anything about mounts.

[odie5533]

How does this interact with caching, will uv sync --frozen --no-install-project rerun when uv.lock changed? https://docs.docker.com/engine/storage/bind-mounts/ doesn't talk about caching and https://docs.docker.com/build/cache/ doesn't say anything about mounts.

It has the same behavior as would adding them to the layer, so if uv.lock or pyproject.toml changes it will re-run the layer (re-run uv sync --frozen --no-install-project).