[docs] Improve docs around configuration

[richardliaw]

We need more polish for the config api, especially the scaling config: • I don’t understand what it is about by looking at this name • it still talks about Ray AIR. • The config itself is not that intuitive. I need to think about it fro a while and then realize that each model replica actor will spawn multiple workers each of which requests those ray resources

[akshay-anyscale]

Some docs improvements here - https://github.com/ray-project/ray-llm/pull/85

[YixuanCao]

+1. I cannot figure out the meaning of these configs. They seem to be inherited from Ray Serve. But I think the ray-llm document should be self-contained.