Add README for typescript demos for indexing (#1276)

This PR adds a comprehensive README file for the TypeScript demos directory, providing documentation for ROS2 communication pattern demonstrations with TypeScript type safety.

- Added detailed documentation explaining three demo categories: topics, services, and actions
- Included structured overview of TypeScript features and development practices
- Created complexity progression table to guide users through learning path

Fix: #1275

Author: minggangw

ts_demo/README.md

@@ -0,0 +1,65 @@
+# TypeScript Demos
+
+This directory contains TypeScript demonstrations showcasing rclnodejs functionality with full type safety and modern development practices. Each demo illustrates core ROS2 communication patterns using TypeScript interfaces and best practices.
+
+## 📂 Available Demos
+
+### 📨 **[topics/](./topics/)** - Publisher/Subscriber Pattern
+
+Basic ROS2 topic communication with TypeScript type safety
+
+- **Publisher**: Sends timestamped string messages at regular intervals
+- **Subscriber**: Receives and displays messages with colorful console output
+- **Features**: Message counting, error handling, graceful shutdown
+
+### 🔧 **[services/](./services/)** - Request/Response Pattern
+
+Synchronous service calls for immediate responses
+
+- **Service Server**: Provides AddTwoInts service for integer addition
+- **Service Client**: Makes requests with random numbers at intervals
+- **Features**: Service discovery, request counting, comprehensive error handling
+
+### ⚡ **[actions/](./actions/)** - Long-Running Task Pattern
+
+Asynchronous actions with progress feedback and cancellation
+
+- **Action Server**: Calculates Fibonacci sequences with progress updates
+- **Action Client**: Sends goals, monitors progress, handles results
+- **Features**: Goal cancellation, feedback processing, result handling
+
+## 🛠️ TypeScript Features
+
+### Type Safety
+
+- **Full typing** for all ROS2 messages, services, and actions
+- **Compile-time validation** of message structures
+- **IntelliSense support** in VS Code and other TypeScript editors
+
+### Modern Development
+
+- **ES2020+ syntax** with async/await patterns
+- **Modular architecture** with clean separation of concerns
+- **Error boundaries** with comprehensive exception handling
+- **Graceful shutdown** handling for SIGINT/SIGTERM
+
+### Code Quality
+
+- **Consistent formatting** with prettier/eslint configurations
+- **Build validation** with TypeScript strict mode
+- **Runtime safety** with proper error handling patterns
+
+## 📊 Complexity Progression
+
+| Demo         | Complexity        | Communication | Best For               |
+| ------------ | ----------------- | ------------- | ---------------------- |
+| **topics**   | ⭐ Basic          | Pub/Sub       | Learning fundamentals  |
+| **services** | ⭐⭐ Intermediate | Req/Response  | Synchronous operations |
+| **actions**  | ⭐⭐⭐ Advanced   | Goal-oriented | Long-running tasks     |
+
+## 🔗 Related Resources
+
+- [rclnodejs Tutorials](../tutorials/) - Comprehensive API documentation
+- [Electron Demos](../electron_demo/) - GUI applications with rclnodejs
+- [TypeScript Handbook](https://www.typescriptlang.org/docs/) - Language reference
+- [ROS2 Documentation](https://docs.ros.org/) - Official ROS2 concepts