Add Paperspace Gradient badges

[glenn-jocher]

Signed-off-by: Glenn Jocher [email protected]

🛠️ PR Summary

_{Made with ❤️ by Ultralytics Actions}

🌟 Summary

Enhancements for YOLOv5 Documentation and CI badges.

📊 Key Changes

• Updated Continuous Integration (CI) badge description for clarity.
• Added a badge and link for running YOLOv5 on Gradient, a cloud computing platform.
• Removed outdated Slack join link from the README files.

🎯 Purpose & Impact

• 📈 Enhanced Clarity: The CI badge text change ("CI CPU testing" to "YOLOv5 CI") makes the badge's purpose clearer to users.
• 🚀 Extended Accessibility: The addition of the Gradient badge provides users another easy-to-access, free GPU environment to run YOLOv5 notebooks.
• 🧹 Cleanup: Removing the Slack link helps avoid confusion as the shared invite may no longer be active, keeping the available communication channels up-to-date.