Add Domain Preview feature documentation

Updated README to describe the new Domain Preview functionality, including workflow changes, feature details, and technical implementation. This provides users and developers with clear instructions and context for previewing domain rules for each service.

README.md

@@ -7,6 +7,7 @@ META.js Customizer is a modern, intuitive web app that allows users to easily cr
 ### ✨ Key Features
 
 - 🔍 **Smart Service Search**: Instantly search and filter through all available services
+- 👁️ **Domain Preview**: Click preview buttons to view domain lists and rules for each service
 - 🎨 **Modern Glass UI**: Beautiful, responsive design with glassmorphism effects
 - 🌙 **Intelligent Theming**: Auto-detects system theme with manual override options
 - 📱 **Mobile Responsive**: Seamlessly adapts to all device sizes
@@ -57,10 +58,41 @@ Visit **[metajs.xi-xu.me](https://metajs.xi-xu.me)** to use the customizer direc
 ### Basic Workflow
 
 1. **🔍 Search for Services**: Use the search bar to find services you want to include
-2. **✅ Select Services**: Click on search results to add them to your configuration
-3. **📝 Review Selection**: Check your selected services in the main panel
-4. **⚙️ Generate Configuration**: Your META.js is automatically generated in real-time
-5. **📋 Copy or Download**: Use the action buttons to copy or download your configuration
+2. **👁️ Preview Domains**: Click "Preview" buttons to see domain rules for each service
+3. **✅ Select Services**: Click on search results to add them to your configuration
+4. **📝 Review Selection**: Check your selected services in the main panel
+5. **⚙️ Generate Configuration**: Your META.js is automatically generated in real-time
+6. **📋 Copy or Download**: Use the action buttons to copy or download your configuration
+
+### 👁️ Domain Preview Feature
+
+The Domain Preview functionality allows you to inspect the domain rules for any service before adding it to your configuration:
+
+#### **Preview Access**
+
+- **Search Results**: Click the "Preview" button next to any service in search results
+- **Selected Services**: Click the "Preview" button next to selected services to review their domains
+
+#### **Domain Categories**
+
+The preview modal organizes domains into three categories:
+
+- **📍 Exact Domains**: Specific domain matches (e.g., `github.com`, `api.github.com`)
+- **🌐 Domain Suffixes**: Wildcard domain patterns that match subdomains (e.g., `+.google.com`)
+- **🔑 Pattern Rules**: Keyword-based and advanced pattern matching rules
+
+#### **Interactive Features**
+
+- **Collapsible Categories**: Click category headers to expand/collapse domain lists
+- **Responsive Design**: Optimized for both desktop and mobile viewing
+- **Real-time Loading**: Fetches latest domain data directly from the RFM repository
+- **Error Handling**: Clear feedback if domain data cannot be loaded
+
+#### **Technical Details**
+
+- **Data Source**: Fetches YAML files directly from [xixu-me/RFM](https://github.com/xixu-me/RFM/tree/universal/yaml)
+- **Smart Parsing**: Automatically categorizes domains based on prefixes and patterns
+- **Glassmorphism UI**: Beautiful modal interface with backdrop blur effects
 
 ### Service Configuration Logic
 
@@ -106,6 +138,15 @@ The META.js Customizer follows a modern, modular architecture designed for maint
 - Implements debounced search for optimal performance
 - Manages service selection state with event-driven updates
 - Provides real-time filtering and search capabilities
+- Integrates domain preview functionality with preview buttons
+
+#### **👁️ DomainPreviewManager**
+
+- Fetches and parses YAML domain files from RFM repository
+- Intelligent domain categorization (exact, suffixes, patterns)
+- Modal-based preview interface with glassmorphism design
+- Real-time domain data loading with error handling
+- Responsive design for mobile and desktop viewing
 
 #### **⚙️ ServiceConfigGenerator**