add README.md for ray service for # 171

[artemisep]

#171, adding README.md for Ray service with the following requirements:

1. A description of what the Ray service is and how it is used in NDIF.
2. Directory structure + explanation of main files.
3. List all the main classes (Controller, Cluster, Node, etc) and give a brief description of what they are.
4. A brief description of the main library dependencies and what they are used for (and remove any that are no longer being used from environment.yml)
5. A list of any relevant environment variables and what they are used for (checkcompose/dev/docker-compose.yml, compose/dev/.env, and the source code).
6. Add a section for spinning up the Ray service from the command line (I can help with providing content). Can mention that it can be spun up but won't work without the API.

[MichaelRipa]

Thanks for contributing! Actually there have been some changes to the ray service (see #196), so we might need to change this a bit. If you have time to take a look and try and make some changes, that would be helpful, but either way I'll start reviewing this PR once the changes are merged into dev (probably later this week).

[artemisep]

Hi @MichaelRipa , Thanks for your input. I have checked out the refactor-deployments branch and created a branch to redo the README.md for ray service and the PR is here: #203. I'm closing this PR. Thanks.