Improve README

[pderrenger]

This pull request attempts to improve the repo README file with additional context and content.

🛠️ PR Summary

_{Made with ❤️ by Ultralytics Actions}

🌟 Summary

Revamped README for better usability and clarity in the Ultralytics xView YOLOv3 repository.

📊 Key Changes

• Improved introduction with more engaging repository description.
• Streamlined installation process: simplified dependency instructions with a pip command.
• Detailed preprocessing steps for clarity before training.
• Described how to start and resume training, emphasizing the import of avoiding overtraining.
• Presented a comprehensive table detailing image augmentations used during training.
• Included instructions for citing the work if used in research.
• Updated visual aesthetics for contributor section and clarified licensing options.

🎯 Purpose & Impact

• 📝 The rewritten documentation aims to make it easier for users to get started with the project, reducing the time to jump from cloning the repo to actual training.
• 🔍 Image augmentation details help users understand the data transformation processes and set expectations for model behavior.
• 🛠️ The explanation of how to manage training progress empowers users to efficiently manage their training sessions.
• 📈 Highlighting overtraining risks provides guidance for achieving optimal model performance.
• 🎓 Citing instructions ensure academic users credit the repository properly, fostering collaboration and recognition of Ultralytics work.
• 📱 Refreshed contributor and license sections offer a cleaner presentation and help users choose the right license for their use case.