Update example for Google OAuth2 offline access

Author: Clément Denis

README.md

@@ -124,14 +124,13 @@ function getDriveService() {
 
       // Sets the login hint, which will prevent the account chooser screen
       // from being shown to users logged in with multiple accounts.
+      // Prefer Session.getEffectiveUser().getEmail() if used in add-ons.
       .setParam('login_hint', Session.getActiveUser().getEmail())
 
       // Requests offline access.
       .setParam('access_type', 'offline')
-
-      // Forces the approval prompt every time. This is useful for testing,
-      // but not desirable in a production application.
-      .setParam('approval_prompt', 'force');
+      // This param is required to ensure a refresh token is always returned.
+      .setParam('prompt', 'consent');
 }
 ```