Add comprehensive README with project overview and setup instructions

Author: scott-the-programmer

README.md

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+# 🎨 Teams Emoji Upload Extension
+
+> Effortlessly bulk upload custom emojis to your Microsoft Teams organization with just a few clicks!
+
+![Screenshot](./readme/screenshot.png)
+
+## ✨ Features
+
+- Bulk upload multiple emoji files simultaneously
+- Works via Teams in the browser
+
+## 📋 Prerequisites
+
+- Active Microsoft Teams tab in Chrome
+
+## 🚀 Installation
+
+### From Chrome Web Store
+
+⏳ Coming soon! Extension is pending approval.
+
+### From Source
+
+1. Clone this repository
+2. Install dependencies and build:
+   ```console
+   npm install
+   npm run build
+   npm test
+   ```
+3. Open Chrome and navigate to `chrome://extensions`
+4. Enable "Developer Mode" in the top right
+5. Click "Load Unpacked" and select this repository folder
+
+![Unpack Instructions](./readme/unpack.png)
+
+> 💡 **Tip**: After making changes, rebuild the project and refresh the extension in Chrome
+
+## 🛠️ Development
+
+### Formatting Code
+```console
+npx prettier . --write
+```
+
+### Running Tests
+```console
+npm test
+```
+
+## 🤝 Contributing
+
+Contributions are welcome! Please feel free to submit a Pull Request.
+
+## 📄 License
+
+[MIT License](LICENSE)