Rework on current book structure

[IAvecilla]

We’re thinking about a new way of organizing all the documentation to make it easier for network users to join a run, which will probably be the most common case, and to place the ‘creating a run’ flow in a separate section. The more in-depth material would go at the end, followed by a more developer-oriented area.

This can serve as a first draft, but we should discuss it further and tweak as needed:

- [Intro to Psyche](./intro.md)

- [Joining a Run]
  - [Requirements]
  - [Quickstart]
  - [Troubleshooting]
  - [End-user FAQ]
  
- [Creating Your Own Run]
  - [Requirements]
  - [Quickstart]
  - [Configuration In Depth]
  - [Authentication]
  - [Run-owner FAQ]
  
- [Psyche In Depth](./explain/index.md)
  - [General Workflow](./explain/general-workflow.md)
  - Run States
    - [Warmup]
    - [Train]
    - [Witness]
    - [Cooldown]
  - [Model Sharing](./explain/model-sharing.md)
  - [Rewards](./explain/rewards.md)
  - [Glossary](./explain/glossary.md)

- [Development](./development/index.md)
  - [Setup & Useful Commands](./development/setup.md)
  - [Running On-chain](./development/running-onchain.md)
  - [Running Off-chain](./development/running-offchain.md)
  - [Implementing Models](./development/models.md)
  - [Python](./development/python.md)
  - [Secrets](./development/agenix.md)
  - [Building These Docs](./development/book.md)
  - [CI](./development/ci.md)
  - [Contributing](./development/contributing.md)