Tracking Issue: New Book Content

With the public release of the official Bevy Book alongside 0.19, we currently have learning content covering most of the core ECS ideas and a handful of periphery ideas for development practices. However, the Bevy engine has a lot more to offer, we just need to write it into the book!

This issue will serve as a tracker for the pages and chapters we want to include in the book, but haven't managed to write out yet. If there's a topic of feature that you think is missing from the book, let us know! Keep in mind though that all pages should be related to features currently implemented in-engine, and that the book targets the **latest Bevy release**. Third party crates or deprecated engine features are not suitable for inclusion.

**New Pages & Chapters**
- Rendering (#2462)
- Animation
- Audio
- Firewheel/Seedling
- Scenes
- BSN
- Input
- UI
- Feathers
- Headless Widgets
- Gizmos
- Development Practices
- Workspace Based Development (#2526)
- Reflection
- `no_std`
- Platform-specific Support/Advice
- Mobile
- ARM/aarch64
- Version Control Setup
- VCS Options
- Why VCS is necessary.

**Existing Content Updates**
- Game Loop Chapter Refresh (#2473)
- #2555
- #2558