docs: update Qwik README with Nixpacks environment variable instructions

qwik/README.md

@@ -10,10 +10,16 @@ This repository contains an example of Qwikjs application that is deployed on Do
    - Publish Directory: `./dist` (Nixpacks)
 
 
-2. **Click on Deploy**:
+2. **Add Environment Variables**:
+- Navigate to the "Environments" tab and add the following variable:
+   ```cmd
+   NIXPACKS_START_CMD="pnpm run preview"
+   ```
+
+3. **Click on Deploy**:
    - Deploy your application by clicking the deploy button.
 
-3. **Generate a Domain**:
+4. **Generate a Domain**:
     - Click on generate domain button.
     - A new domain will be generated for you.
     - You can use this domain to access your application.