docs: update README with features and usage

Author: wsqstar

readme.md

@@ -0,0 +1,58 @@
+# Mermaid Parser
+
+A minimal online Mermaid diagram parser for creating, previewing, and exporting diagrams.
+
+**Live Demo**: https://mappedinfo.github.io/mermaidreader/
+
+## Features
+
+- **Real-time Preview** - Diagrams render instantly as you type
+- **Zoom Controls** - Zoom in/out (25%-400%) with reset option
+- **Resizable Preview** - Drag to resize the preview area
+- **Copy Text** - Copy Mermaid syntax to clipboard
+- **Export Image** - Export diagrams as 300 DPI PNG
+- **Error Display** - Detailed syntax error messages with location
+
+## Usage
+
+1. Paste or type Mermaid syntax in the text area
+2. View the rendered diagram in the preview
+3. Use zoom controls (+/-) to adjust size
+4. Click "Copy Text" or "Copy Image" to export
+
+## Supported Diagram Types
+
+- Flowchart
+- Sequence Diagram
+- Class Diagram
+- State Diagram
+- Entity Relationship Diagram
+- Gantt Chart
+- Pie Chart
+- Git Graph
+- Mind Map
+- Timeline
+- And more...
+
+## Development
+
+```bash
+# Install dependencies
+npm install
+
+# Start dev server
+npm run dev
+
+# Build for production
+npm run build
+
+# Preview production build
+npm run preview
+```
+
+## Tech Stack
+
+- Vite
+- TypeScript
+- Mermaid.js
+- GitHub Pages