docs: Add README.md with project description and usage instructions

Author: splitbrain

README.md

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+# PCB Pinout Diagram Generator
+
+This project generates Scalable Vector Graphics (SVG) pinout diagrams for Printed Circuit Boards (PCBs) based on configuration files written in YAML or JSON. It provides both a web-based editor for interactive diagram creation and a command-line interface (CLI) for batch processing.
+
+## Features
+
+*   **SVG Output:** Generates clean, scalable SVG diagrams.
+*   **Configuration:** Define pinouts, board dimensions, labels, and types using simple YAML or JSON files.
+*   **Web Editor:**
+    *   Real-time preview of the diagram as you edit the configuration.
+    *   Syntax highlighting for YAML.
+    *   Load configurations from local files, URLs, or browser storage.
+    *   Download generated SVG diagrams (front and back views).
+*   **CLI Tool:** Process multiple configuration files or entire directories to generate SVG diagrams programmatically.
+*   **Image Embedding:** Embed background images (e.g., photos of the PCB) from local paths or URLs directly into the SVG. Supports front and back images.
+*   **Customization:** Define custom types for pins with specific background and foreground colors, automatically generating a legend.
+*   **Front & Back Views:** Automatically generates diagrams for both the front and back sides of the PCB.
+
+## Usage
+
+### Web Editor
+
+1.  Open `public/index.html` in your web browser (requires a local web server or building the project).
+2.  Edit the YAML configuration in the editor pane.
+3.  The SVG diagram preview will update automatically.
+4.  Use the "Download SVG" buttons below each preview to save the front or back view.
+
+### Command-Line Interface (CLI)
+
+1.  Ensure you have Node.js installed.
+2.  Run the CLI tool with configuration files or directories as arguments:
+
+    ```bash
+    node src/cli.js path/to/your/config.yaml path/to/another/config.json some/directory/
+    ```
+3.  The tool will generate corresponding `.svg` files (e.g., `config.front.svg`, `config.back.svg`) in the same directory as the input files.
+
+## Configuration
+
+Diagrams are configured using YAML or JSON files. Key sections include:
+
+*   `title`: The title displayed on the diagram.
+*   `width`, `height`: Board dimensions in number of pins.
+*   `pins`: Defines pin labels and types for `left`, `right`, `top`, `bottom` rows.
+*   `types`: Custom pin type definitions (colors).
+*   `image`: Configuration for embedding background images (front/back).
+
+See the example files in `public/pinouts/` for detailed structure.
+
+## Development
+
+1.  Install dependencies:
+    ```bash
+    npm install
+    ```
+2.  Build the project (for web editor and CLI):
+    ```bash
+    node build.js
+    ```
+3.  Start the development server with hot reloading for the web editor:
+    ```bash
+    node build.js --serve
+    ```
+
+```