docs(Storage): explain what the plugin uses under the hood (#2058)

site/docs-md/apis/storage/index.md

@@ -15,6 +15,8 @@ The Storage API provides a key-value store for simple data.
 
 Mobile OS's may periodically clear data set in `window.localStorage`, so this API should be used instead of `window.localStorage`. This API will fall back to using `localStorage` when running as a Progressive Web App.
 
+On iOS this plugin will use [UserDefaults](https://developer.apple.com/documentation/foundation/userdefaults) and on Android [SharedPreferences](https://developer.android.com/reference/android/content/SharedPreferences). Stored data is cleared if the app is uninstalled.
+
 Note: this API is not meant for high-performance data storage applications. Take a look at using SQLite or a separate data engine if your application will store a lot of items, have high read/write load, or require complex querying.
 
 <plugin-api index="true" name="storage"></plugin-api>