Add integration example with YAML configuration file

[hirotask]

Summary

Add a sample demonstrating how to integrate the flagly with a YAML configuration file.

Motivation

Providing a concrete YAML integration example helps users quickly understand how to configure and use the project in real-world scenarios. Without examples, users may struggle with setup and configuration, leading to poor developer experience.

Definition of done

• A YAML configuration example is added in the example directory.
• The example clearly demonstrates how to integrate with the flagly.
• The configuration is validated and works as expected.

Proposed approach

1. Create a sample YAML file (e.g., config.yaml).
2. Define required and optional configuration fields.
3. Provide inline comments or documentation explaining each field.
4. Add usage instructions in the README.
5. Optionally include a minimal working example that uses the YAML configuration.

Additional context

Example of a yaml file:

features:
  featureA:
    enabled: true
  featureB:
    enabled: true
  featureC:
    enabled: true

Ensure the example reflects actual use cases and stays in sync with the codebase.

Related issues

N/A