🐛 Fix critical borrow checker bug + 📚 Enhance README documentation

[melotik]

🔧 Critical Bug Fix + Documentation Enhancement

This PR addresses a critical compilation bug in the borrow checker exercise and significantly improves the project's documentation.

🐛 Bug Fix: Borrow Checker Lifetime Issue

The Problem

The 3-borrow-checker/src/main.rs file contained a fatal lifetime bug that prevented compilation:

// ❌ BROKEN CODE
fn main() {
    let name1 = String::from("Pranav");
    let bigger = {
        let name2 = String::from("Tiago");  // ⚠️ name2 scope starts here
        let bigger = bigger_string(&name1, &name2);
        bigger;  // ⚠️ name2 scope ends here, but bigger might reference it!
    };
    println!("The bigger string is: {bigger}");  // 💥 COMPILATION ERROR
}

The Root Cause

Rust's borrow checker detected that:

1. name2 goes out of scope at the end of the inner block
2. The bigger variable might contain a reference to name2
3. Using bigger after name2 is dropped violates memory safety rules

✅ The Fix

Moved both string declarations to the same scope level:

// ✅ FIXED CODE
fn main() {
    let name1 = String::from("Pranav");
    let name2 = String::from("Tiago");  // Both strings in same scope
    
    // Both strings live long enough for the returned reference to be valid
    let bigger = bigger_string(&name1, &name2);
    
    println!("The bigger string is: {}", bigger);  // ✅ Compiles successfully
}

Impact

• Before: Code would not compile due to lifetime violation
• After: Code compiles and runs correctly, demonstrating proper borrowing patterns
• Educational value: Shows learners real-world borrow checker solutions

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📚 Documentation Enhancement: README Overhaul

The Problem

The original README was extremely minimal:

# Rust Bootcamp

Learning rust to build substreams.

This provided no guidance for learners and made the repository hard to navigate.

✅ The Enhancement

Created a comprehensive, professional README with:

🎯 Clear Learning Objectives

• Defined specific Rust concepts covered
• Connected learning to substreams development

📚 Structured Course Overview

• Detailed description of each exercise directory
• Learning concepts for each section
• Progressive difficulty indication

🚀 Getting Started Guide

• Prerequisites and setup instructions
• Step-by-step running instructions
• Suggested learning path

🔧 Development Setup

• IDE recommendations with extensions
• Useful cargo tools and commands
• Auto-reload development workflow

📖 Additional Resources

• Links to official Rust documentation
• Learning materials and references
• Substreams specific resources

🤝 Contributing Guidelines

• Clear process for making improvements
• Encourages community contributions

Impact

• Accessibility: Makes the repository welcoming to newcomers
• Navigation: Clear structure helps learners progress systematically
• Professional: Repository now has documentation quality matching its educational value
• Discoverability: Better SEO and GitHub search visibility

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🧪 Testing Done

✅ Compilation Test: Verified the fixed borrow checker code compiles and runs correctly
✅ Documentation Review: Ensured all links work and formatting is consistent
✅ Structure Validation: Confirmed all mentioned directories and files exist

📈 Benefits

1. Immediate: Fixes a blocking compilation error that prevented learning
2. Long-term: Professional documentation attracts more contributors and learners
3. Educational: Both fixes demonstrate best practices in Rust development
4. Maintenance: Clear contributing guidelines encourage future improvements

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Ready for review! This PR makes the rust-bootcamp repository significantly more valuable for Rust learners. 🚀