Fixed .env copy command

Author: dean-journeyapps

demos/react-native-background-sync/README.md

@@ -28,7 +28,7 @@ cd demos/react-native-background-sync
 Set up the Environment variables: Copy the `.env` file:
 
 ```bash
-cp .env .env.local
+cp .env.local.template .env.local
 ```
 
 And then edit `.env.local` to insert your credentials for `Supabase`.