Merge pull request #18 from guillemc23/patch-1

Update README.md

Author: triniwiz

packages/firebase-core/README.md

@@ -5,6 +5,7 @@ ns plugin add @nativescript/firebase-core
 ```
 
 ## Usage
+Make sure you have your `google-services.json` file located in `App_Resources/src`.
 
 ### Initialize Default App