Update README with usage instructions

README.md

@@ -1,3 +1,30 @@
+# Solar System 3D Simulation
+
+This project provides a simple 3D visualization of the solar system built with [Three.js](https://threejs.org/). It renders the Sun, planets and their moons with controls for adjusting the view and simulation speed. The interface supports both desktop and mobile devices.
+
+## Prerequisites
+
+- A modern web browser with JavaScript enabled and WebGL support (Chrome, Firefox, Safari, Edge, etc.).
+- Optionally, a small HTTP server if you want to avoid potential cross-origin restrictions when opening files directly from disk.
+
+## Running the Demo
+
+1. Clone or download this repository.
+2. Open `index.html` in your browser. You can double‑click the file or serve it via a local web server.
+3. If textures or other resources fail to load when opened directly, start a simple server from the project directory and browse to `index.html` from that server. For example using Python 3:
+
+   ```bash
+   python3 -m http.server 8000
+   ```
+
+   Then visit `http://localhost:8000/index.html` in your browser.
+
+## Usage
+
+Use your mouse (or touch on mobile) to rotate, zoom and explore the planets. Additional controls are available in the on-screen panel.
+
+Enjoy exploring the solar system!
+=======
 # solarsystem
 
 ## Running tests
@@ -11,3 +38,4 @@ python3 validate_html.py
 
 The same script runs automatically in CI when you open a pull request or push
 changes.
+