Fix changes

Changes:

- Added sections with diagrams and their descriptions.
- Changed descriptions of some components, such as Scheduler and Reactor.
- Added a new section "Spawn with child expression" with code examples.
- Updated code examples for various expressions, such as `spawn` and `suspend`.
- Added new diagram files: decision-tree.puml and feature-to-requirement.puml, as well as their corresponding SVG versions.

These changes include improvements to the documentation, addition of new features, and clarification of existing descriptions and examples.