added new commands to run app

with new gradle build script

Author: SGI-CAPP-AT2

CONTRIBUTING.md

@@ -38,7 +38,11 @@ flutter pub get
 5. Run the app:
 
 ```bash
-flutter run
+flutter run --flavor production
+```
+Also Check if it's working with nightly with
+```bash
+flutter run --flavor nightly
 ```
 
 ### Check out the app