Add flow template generator documentation for meta-skill/flow-coordinator

- Introduced a comprehensive guide for generating workflow templates.
- Detailed usage instructions with examples for creating templates.
- Outlined execution flow across three phases: Template Design, Step Definition, and JSON Generation.
- Included JavaScript code snippets for each phase to facilitate implementation.
- Provided suggested step templates for various development scenarios.
- Documented command port references and minimum execution units for clarity.

Author: catlog22