adds setting screen

src/application/main-window.vala

@@ -24,6 +24,15 @@ public class MainWindow : Adw.ApplicationWindow
 
         var transcript_page = new NavigationPage (transcript_view, "Transcript");
         split_view.content = transcript_page;
+
+        var show_settings_action = new SimpleAction ("settings", null);
+        show_settings_action.activate.connect(show_settings);
+        add_action(show_settings_action);
+    }
+
+    private void show_settings () {
+        var dialog = new PreferencesWindow (this);
+        dialog.present (this);
     }
 
     private void conversation_selected(string? conversation_guid) {