Add DocsGPT to the list of projects for beginners

- DocsGPT is an open-source RAG assistant for reliable document Q&A
- 16.9k stars, 195 contributors, actively maintained with modern AI/ML stack
- Uses 'good first issue' label with currently 3 open beginner-friendly issues
- Built with Python (40.7%) and TypeScript (52.6%)
- Repository: https://github.com/arc53/DocsGPT