Add keychainAccessGroup configuration option (#36)

Author: thorrak

README.md

@@ -40,7 +40,8 @@ startActivity(3, "4343", "$32.23", driverName, 47, 43);
 - `frequentUpdates` (boolean, default: false): Depending on this param, NSSupportsLiveActivitiesFrequentUpdates will be set
 - `widgetsFolder` (string, default: "widgets"): Path from the project root to the folder containing the Swift widget files
 - `deploymentTarget` (string, default: "16.2"): The minimum deployment target for the app
-- `groupIdentifier` (string): The app group identifier which is required for communication with the main app. Must start with `group.`
+- `groupIdentifier` (string, optional): The app group identifier which is required for communication with the main app. Must start with `group.`
+- `keychainAccessGroup` (string, optional): A keychain access group if you want to securely share secrets. Should start with your `<TEAM_ID>.`
 <!--
 - `moduleFileName` (string, default: "Module.swift"): File within the widget folder that defines the native module
 - `attributesFileName` (string): File within the widget folder that defined the widget attributes