added method invalidInput

src/TextOutput.java

@@ -130,4 +130,11 @@ public class TextOutput {
     public void errorInvalidCommand() {
         System.err.println("Invalid Command");
     }
+
+    /**
+     * Method to give out the Error "Invalid Input".
+     */
+    public void invalidInput() {
+        System.err.println("Invalid Input");
+    }
 }