Documentation bug: retrain group referenced in retraining guide but missing from resources_config.yaml

[Hanzo-Huang]

Problem Description

The retraining example documentation in doc/developer_guide/retraining_example.md instructs users to run hailo-download-resources --group retrain, but the retrain group does not exist in resources_config.yaml. This causes the download command to fail with the error: Group 'retrain' not found in config.

Steps to Reproduce

1. Follow the retraining example guide in doc/developer_guide/retraining_example.md
2. Run the command: hailo-download-resources --group retrain
3. Observe the error: Group 'retrain' not found in config