Add .env.example in hello-world app (#15211)

as title

packages/twenty-apps/hello-world/.env.example

@@ -0,0 +1 @@
+TWENTY_API_KEY=<SET_YOUR_TWENTY_API>

packages/twenty-apps/hello-world/README.md

@@ -14,6 +14,10 @@ This example will gradually gain complexity and capabilities as the twenty-cli m
 
 ## Install to your Twenty workspace
 
+```bash
+cp .env.example .env
+```
+
 - replace `<SET_YOUR_TWENTY_API>` with your apiKey
 
 ```bash