add the Main class to this project

app/src/main/java/org/cutem/cutecalendar/Main.java

@@ -0,0 +1,16 @@
+package org.cutem.cutecalendar;
+
+import javafx.application.Application;
+import javafx.stage.Stage;
+
+public class Main extends Application {
+
+    public static void main(String[] args) {
+        launch(args);
+    }
+
+    @Override
+    public void start(Stage primaryStage) {
+        primaryStage.show();
+    }
+}