docs: update README.md with GOOGLE_SERVICES_B64 docs

README.md

@@ -43,17 +43,12 @@ cd metamask-mobile
 
 Before running the app, keep in mind that MetaMask uses FCM (Firebase Cloud Message) to empower communications. Based on this, as an external contributor you would preferably need to provide your own FREE Firebase project config file with a matching client for package name `io.metamask`, and update your `google-services.json` file in the `android/app` directory as well your `.env` files (`.ios.env`, `.js.env`, `.android.env`), adding `GOOGLE_SERVICES_B64` variable depending on the environment you are running the app (ios/android).
 
-The value you should provide to `GOOGLE_SERVICES_B64` is the base64 encoded version of your Firebase project config file, which can be generated as follows:
+ATTENTION: In case you don't provide your own Firebase project config file, you can make use of a mock file at `android/app/google-services-example.json`, following the steps below from the root of the project:
 
 ```bash
-base64 -w0 -i ./android/app/google-services-example.json
+echo "export GOOGLE_SERVICES_B64=\"$(base64 -w0 -i ./android/app/google-services-example.json)\"" | tee -a .js.env .ios.env .android.env
 ```
 
-Copy the result to your clipboard and paste it in the `GOOGLE_SERVICES_B64` variable in the `.env` file you are running the app.
-
-> [!CAUTION]
-> In case you don't provide your own Firebase project config file, you will face the error `No matching client found for package name 'io.metamask'`.
-
 You can make usage of a mock file at `android/app/google-services-example.json`, following the same steps above from the root of the project.
 
 In case of any doubt, please follow the instructions in the link below to get your Firebase project config file.