[Feature]: Documentation for Loops and Conditionals

### Feature Request

Rivet is absolutely awesome, but I've decided to use Flowise till I can figure out how to:
- Executed branches based on whether a Code node returns true or false
- Loop based on the return value of a Code node.

### Code of Conduct

- [X] I agree to follow this project's Code of Conduct

No files, tests, or documentation entry points are named in the issue. Start by locating the existing documentation for Code nodes, branching, and loops; document how branches depend on a Code node returning true or false and how loop continuation depends on its return value.

Written by the indexing model from the issue text.