docs: add Getting Started tutorial for new contributors (Bounty #830)

[liqiuniu]

Summary

Complete beginner's guide to earning by contributing to SolFoundry. Addresses Bounty #830.

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What's Included

A comprehensive GETTING_STARTED.md tutorial covering:

For New Contributors

Section	Content
Prerequisites	Git, GitHub account, code editor setup
Wallet Setup	Phantom installation, getting wallet address
Finding Bounties	Browsing issues, using gh CLI, understanding labels
Fork & Clone	Repository setup, branch creation
Building Solutions	Dev environment, linters, committing
Submitting PRs	PR format, wallet requirement, Closes #N

Understanding the Platform

Section	Content
AI Review Process	How 5 AI models score your code
Bounty Tiers	T1/T2/T3 differences, progression path
Scoring Thresholds	Pass requirements by tier
Tier Progression	How to unlock T2 and T3

Practical Help

Section	Content
Tips for Success	Best practices checklist
Common Mistakes	What to avoid with examples
FAQ	Answers to common questions

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Features

• Step-by-step instructions 鈥?Every step from wallet setup to first PR
• Clear formatting 鈥?Tables, code blocks, diagrams
• Visual tier progression 鈥?ASCII diagram showing T1 鈫?T2 鈫?T3 path
• Practical examples 鈥?Correct vs incorrect PR format
• Beginner-friendly language 鈥?No jargon, clear explanations

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Acceptance Criteria

• Complete tutorial covering the full contributor flow
• Clear, beginner-friendly language
• Diagrams/tables included (ASCII diagrams, comparison tables)

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Testing

1. Read through docs/GETTING_STARTED.md
2. Verify all sections are clear and complete
3. Check all links work
4. Confirm formatting renders correctly in GitHub markdown

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Related

Bounty #830 鈥?#830