Add example env file and clarify setup steps

.env.example

@@ -0,0 +1,2 @@
+# Copy this file to .env.local and set your Gemini API key
+VITE_API_KEY=your_key_here

README.md

@@ -15,6 +15,6 @@ View your app in AI Studio: https://ai.studio/apps/drive/1a8wkyYOUvPDWvUXbrtN2dz
 
 1. Install dependencies:
    `npm install`
-2. Set the `VITE_API_KEY` in [.env.local](.env.local) to your Gemini API key (e.g., `VITE_API_KEY=your_key_here`)
+2. Copy `.env.example` to `.env.local` and set `VITE_API_KEY` to your Gemini API key (e.g., `VITE_API_KEY=your_key_here`).
 3. Run the app:
    `npm run dev`