Address followup comments from https://github.com/ray-project/ray/pull/19863
- Add short "Concepts" section
- Add more section headings to break up the text
- Add "Workflow: Local Files" example
- Add "Workflow: Library development" example
* Small improvements to the Ray Cluster docs
* Update quickstart.rst
Changed title for quick start
Co-authored-by: Javier Redondo <javier@Anyscale-MacBook-Pro.local>