docs: improve homepage with metadata, accessibility, and better layout

[aman689]

Summary

This PR improves the documentation homepage for Supervision.

Changes

• Added SEO metadata (title, description)
• Added alt text to banner image for accessibility
• Replaced empty H1 with descriptive heading
• Improved “Hello” section grammar
• Added “Documentation Overview” and “Join the Community” sections
• Fixed Markdown formatting for “Filter Objects in Zone”

Why

These changes enhance readability, accessibility, and navigation for new users.

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🧩 Part of #Hacktoberfest 2025

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