Add docs for template system

Author: Reason-Wang

docs/chat_template/README.md

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+# Chat Template System
+
+To enable Agent-RL for various models, we have supported a powerful and flexible template system inspired by building block toys, designed to support various ways of forming conversation templates for large language models.
+
+## Overview
+
+The Chat Template System is a comprehensive framework that provides a modular, extensible approach to creating conversation templates. It's designed with the philosophy that complex templates can be built from simple, reusable components - much like building blocks that can be combined in countless ways.
+
+## Key Features
+
+- **Modular Design**: Templates are built from configurable components
+- **Multi-Modal Support**: Built-in vision and video processing capabilities
+- **Tool Integration**: Flexible tool placement and formatting strategies
+- **Policy-Based Configuration**: System and tool policies for fine-grained control
+- **Jinja Template Generation**: Automatic HuggingFace-compatible template generation
+- **Extensible Architecture**: Easy to add new template types and processors
+
+## Quick Start
+
+```python
+from agents.agents.agents.templates import Chat, get_template
+
+# Get a pre-built template
+template = get_template("qwen2.5")
+
+# Create a chat instance
+chat = Chat(template="qwen2.5", messages=[
+    {"role": "user", "content": "Hello, how are you?"}
+])
+
+# Generate a prompt
+prompt = chat.prompt()
+print(prompt)
+```
+
+## Documentation Structure
+
+- [**Architecture & Design**](./architecture.md) - System design philosophy and architecture
+- [**Basic Usage**](./basic_usage.md) - Getting started with templates
+- [**Custom Templates**](./custom_templates.md) - Creating your own templates
+- [**Advanced Features**](./advanced_features.md) - Tool policies, system policies, and more
+- [**Vision Templates**](./vision_templates.md) - Multi-modal template support
+- [**Examples**](./examples.md) - Practical examples and use cases
+
+## Core Concepts
+
+### Template Components
+- **System Template**: Defines the system message format
+- **User Template**: How user messages are formatted
+- **Assistant Template**: How assistant responses are formatted
+- **Tool Template**: How tool responses are formatted
+
+### Policies
+- **System Policy**: Controls system message behavior
+- **Tool Policy**: Manages tool placement and formatting
+- **Global Policy**: Global template behavior settings
+
+### Vision Support
+- **Image Processing**: Automatic image token expansion
+- **Video Processing**: Video frame extraction and processing
+- **Multi-Modal Alignment**: Proper tensor alignment for training
+
+## Getting Help
+
+For questions and issues:
+- Check the examples in the [Examples](./examples.md) section
+- Review the [Advanced Features](./advanced_features.md) for complex use cases
+- Examine the source code in `agents/agents/agents/templates/`
+
+## Contributing
+
+The template system is designed to be extensible. See [Custom Templates](./custom_templates.md) for guidance on adding new template types and processors.