Add docstrings to YOLOv5 functions

[glenn-jocher]

🛠️ PR Summary

_{Made with ❤️ by Ultralytics Actions}

🌟 Summary

This PR introduces comprehensive in-code documentation across multiple Python files in the Ultralytics YOLOv5 repository.

📊 Key Changes

• Added docstrings to functions in benchmarks.py, detect.py, export.py, hubconf.py, train.py, and val.py to describe their purpose, arguments, and behavior.
• No changes to functional code, ensuring that the actual behavior of the YOLOv5 models and utilities remains unchanged.

🎯 Purpose & Impact

• Enhanced Readability & Maintenance: Clear descriptions make the codebase more accessible and easier to maintain, especially for new contributors and developers.
• Better User Understanding: Helps non-expert users to understand the functionalities and usages of the different scripts and functions within the YOLOv5 project.
• No Impact on Model Performance: Since there are no functional changes, users will experience no difference in the performance or outputs of their YOLOv5 models.