docs(contributing): add quick-start demo asset to onboarding guide

[techAlhaji]

Summary

Closes #146

Adds a visual onboarding asset demonstrating the basic contributor workflow (clone → test → demo) and links it from CONTRIBUTING.md to help first-time contributors get started more quickly.

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What Changed

🎥 Quick-Start Demo Asset

Added a visual asset illustrating the typical contributor workflow:

1. Clone the repository
2. Install dependencies
3. Run tests
4. Build the project
5. Launch the demo/application

The asset provides a quick reference for new contributors before they begin making changes.

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📚 CONTRIBUTING.md

Updated CONTRIBUTING.md to include:

• A link to the quick-start demo asset
• A short description of what the demo covers
• Guidance for first-time contributors on where to begin

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Benefits

• Improves the onboarding experience for new contributors
• Reduces setup confusion
• Provides a visual reference alongside written instructions
• Makes the contribution workflow easier to follow

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Testing

Documentation-only change.

No application behavior or contract logic was modified.

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Checklist

• Added onboarding/demo asset
• Linked asset from CONTRIBUTING.md
• Documentation reviewed for clarity
• No functional code changes
• CI checks remain green