Ensures weights/ dir exists

[KPLauritzen]

Allows train.py to be run outside of yolov5/ directory.

Otherwise this requires the user to make a directory called weights/ in the working directory.

🛠️ PR Summary

_{Made with ❤️ by Ultralytics Actions}

🌟 Summary

Enhanced training script to ensure weights directory exists.

📊 Key Changes

• Added a line of code to create the 'weights' directory if it does not exist.

🎯 Purpose & Impact

• 🛠️ Purpose: Prevents potential errors or crashes that could occur if the 'weights' directory, where model weights are saved during training, is missing.
• 🔁 Impact: Users experience a more robust and error-proof training process, as the script now automatically handles directory creation.

[glenn-jocher]

Good idea, thank you!