Add beginner learning resources for GitHub fundamentals

[Copilot]

Repository needed beginner-friendly materials for users starting to learn GitHub.

Changes

New Documentation Files

• GETTING_STARTED.md - Core concepts (repository, branch, commit, PR, merge), terminology glossary, first steps guide
• CHEAT_SHEET.md - Web interface operations, CLI commands with syntax, workflow patterns, common issues reference
• TROUBLESHOOTING.md - 10+ common beginner problems with solutions, error resolution patterns, help resources

README Updates

• Added navigation section linking to all learning resources
• Added "New to GitHub?" callout directing beginners to getting started guide
• Added "Additional Learning Resources" section for post-course learning

Structure

All resources are standalone and progressively detailed:

• README → high-level course overview
• GETTING_STARTED.md → concepts before hands-on
• CHEAT_SHEET.md → ongoing reference
• TROUBLESHOOTING.md → self-service problem resolution

Original course workflow and GitHub Actions automation unchanged.

Original prompt

I am starting to learn how to use Github

---

💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more Copilot coding agent tips in the docs.