Add showcase with model to usage section

Author: AB-xdev

README.md

@@ -18,12 +18,20 @@ For more and detailed usage examples please have a look at [the demo](./vaadin-c
 
 ```java
 // Assumes that this code is in some kind of Vaadin component or view
-
 ChartContainer chart = new ChartContainer();
 this.add(chart);
 
 chart.showChart(
   "{\"data\":{\"labels\":[\"A\",\"B\"],\"datasets\":[{\"data\":[1,2],\"label\":\"X\"}]},\"type\":\"bar\"}");
+
+// Or utilizing chartjs-java-model
+chart.showChart(new BarChart(new BarData()
+  .addLabels("A", "B")
+  .addDataset(new BarDataset()
+    .setLabel("X")
+    .addData(1)
+    .addData(2)))
+  .toJson());
 ```
 
 ### Recommended