add README.md for ray service based on refactor-deployments branch for #171

[artemisep]

redo #171,
#198, based on refactor-deployments branch #196.
requirement from #171:

Description

Currently, the Ray service is missing basic documentation. A README should be added which includes the following:

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]

@artemisep Quick update, I just completely removed src/services/ray/src/ray/distributed, so this can be removed from the README 🙂 It was completely outdated and just overall made the codebase less readable