Replace nvidia-docker dependency with plain docker.

[tkunic]

Background

When SMILER was created, nvidia-docker was the only reasonably-easy way to attach GPUs to containers. However, today, plain docker seems to support everything SMILER needs:

• https://docs.docker.com/config/containers/resource_constraints/#access-an-nvidia-gpu
• https://docs.docker.com/compose/gpu-support/

It'd be nice to replace nvidia-docker with plain docker users are likely to already have set up on their systems, so we can reduce the setup burden for our users.

Acceptance Criteria

• smiler run does not interact with nvidia-docker any more.
• README.md and SMILER setup documentation have been updated with new nvidia-dockerless process.