show screenshots in tutorial

src/main/java/ch/zhaw/gartenverwaltung/TutorialController.java

@@ -1,6 +1,7 @@
 package ch.zhaw.gartenverwaltung;
 
 
+import ch.zhaw.gartenverwaltung.io.PlantList;
 import javafx.fxml.FXML;
 import javafx.scene.control.Button;
 import javafx.scene.image.Image;
@@ -8,6 +9,7 @@ import javafx.scene.image.ImageView;
 import javafx.scene.layout.StackPane;
 import javafx.stage.Stage;
 import java.io.File;
+import java.io.InputStream;
 
 /**
  * Controller class for the Tutorial.fxml file
@@ -46,10 +48,10 @@ public class TutorialController {
      * @param fileName the file name of the source
      */
     private void setImageView(ImageView imageView, String fileName) {
-        File file = new File(String.valueOf(PlantsController.class.getResource(fileName)));
+        InputStream is = PlantsController.class.getResourceAsStream("screenshots/" + fileName);
         Image image;
-        if (file.exists()) {
-            image = new Image(String.valueOf(PlantsController.class.getResource(fileName)));
+        if (is != null) {
+            image = new Image(String.valueOf(PlantsController.class.getResource("screenshots/" + fileName)));
         } else {
             image = new Image(String.valueOf(PlantsController.class.getResource("placeholder.png")));
         }