TICKET-T-19790: Updated the app build steps in readme (heremaps#119)

Signed-off-by: Rahul Pant <[email protected]>

README.md

@@ -70,13 +70,16 @@ Create a file .env/dev.json as:
 If you are new to Flutter, here are more detailed steps for you. You may also want to consult the official [Flutter](https://flutter.dev) site in general and the [Flutter SDK](https://flutter.dev/docs/development/tools/sdk/overview) documentation in particular first.
 
 - Build for Android:
-  - Build an Android APK by executing `flutter build apk` or use the command `flutter run` to build and run on an attached device.
+  - Build an Android APK by executing `flutter build apk --dart-define-from-file=.env/dev.json` or use the command `flutter run --dart-define-from-file=.env/dev.json` to build and run on an attached device.
 - Build for iOS:
   - Run `pod install` in the [ios folder](./ios/).
-  - Then go back to the repository root folder and type `flutter build ios` to build a Runner.app. Type `flutter run` to build and run on an attached device.
+  - Then go back to the repository root folder and type `flutter build ios --dart-define-from-file=.env/dev.json` to build a Runner.app. Type `flutter run --dart-define-from-file=.env/dev.json` to build and run on an attached device.
   - You can open the `/repository root/ios/Runner.xcworkspace` project in Xcode and execute and debug from there.
   - Note: You need to have valid _development certificates_ available to sign the app for device deployment.
 
+Note: You can alternatively also pass the credentails during build by: 
+`flutter build apk --dart-define=HERESDK_ACCESS_KEY_ID=<YOUR_ACCESS_KEY_ID> --dart-define=HERESDK_ACCESS_KEY_SECRET=<YOUR_ACCESS_KEY_SECRET>`
+
 ## Contributing
 
 You can contribute to this open source project and improve it for others. There are many ways to contribute to this project, whether you want to create an issue, submit bug reports or improve the documentation - we are happy to see your merge requests. Have a look at our [contribution guide](./CONTRIBUTING.md) and [code of conduct](./CODE_OF_CONDUCT.md). Happy coding!