Add Project Structure Documentation to README #346

Problem

The README.md currently lacks a clear project structure section that shows the organization of files and directories. This makes it difficult for new contributors to understand where different components are located and how the project is organized.

Proposed Solution

Add a comprehensive "Project Structure" section to the README.md that visualizes the directory tree and explains the purpose of each major folder/file.

Acceptance Criteria

• Add a "📁 Project Structure" section in README.md (preferably after Features and before Contributing)
• Include a visual directory tree showing main folders and key files
• Add brief descriptions for each major directory/component
• Use proper markdown formatting with code blocks
• Ensure the structure matches the actual repository organization
• Keep it concise but informative (not every single file, just important ones)

Suggested Format

## 📁 Project Structure

jarvis/
├── .streamlit/ # Streamlit configuration files
├── models/ # ML/DL model implementations
│ ├── BrainTumorModel/ # Brain tumor detection
│ ├── DiabetesModel/ # Diabetes prediction
│ └── ... # Other model modules
├── utils/ # Helper functions and utilities
│ ├── authentication.py # Auth logic
│ └── voice_handler.py # Voice command processing
├── ui/ # UI components (if applicable)
├── assets/ # Images, demos, screenshots
├── app.py # Main Streamlit application
├── requirements.txt # Python dependencies
├── secrets.example.toml # Template for API keys/secrets
├── .gitignore # Git ignore rules
├── LICENSE # Project license
└── README.md # Project documentation