Add README section about "App groups"

Author: Christoph Pader

README.md

@@ -317,6 +317,14 @@ You can specify flags via `<PROJECT_ROOT>/android/gradle.properties` like so:
 quickSqliteFlags="<SQLITE_FLAGS>"
 ```
 
+## Additional configuration
+
+### App groups (iOS only)
+
+On iOS, the SQLite database can be placed in an app group, in order to make it accessible from other apps in that app group. E.g. for sharing capabilities.
+
+To use an app group, add the app group ID as the value for the `ReactNativeQuickSQLite_AppGroup` key in your project's `Info.plist` file. You'll also need to configure the app group in your project settings. (Xcode -> Project Settings -> Signing & Capabilities -> Add Capability -> App Groups)
+
 ## Oscar
 
 react-native-quick-sqlite was originally created by [Oscar Franco](https://github.com/ospfranco). Thanks Oscar!