Add Docker --file argument to build

[glenn-jocher]

https://docs.docker.com/engine/reference/commandline/build/

🛠️ PR Summary

_{Made with ❤️ by Ultralytics Actions}

🌟 Summary

Refinement of Docker build commands in the Ultralytics YOLOv5 repository.

📊 Key Changes

• Explicitly specified Dockerfile paths in the build commands for GPU and CPU Docker images.

🎯 Purpose & Impact

• 🛠 Purpose: Ensures clarity and correctness when building Docker images, especially in cases where Docker is run from a directory different from the Dockerfile's location.
• 🚀 Impact: Users have improved guidance for building Docker images, reducing the chance of errors and increasing convenience.