Add example how SVG creation works in the hpainter batch

Author: linev

demo/node/hpainter.js

@@ -1,3 +1,7 @@
+// demo how HierarchyPainter can be used without direct display
+// in batch display one just able to create images
+
+
 import { version, HierarchyPainter, draw } from 'jsroot';
 
 
@@ -25,3 +29,14 @@ await hp.expandItem('ntuple');
 // invoking TTree::Draw
 await hp.display('ntuple/pz');
 
+
+// should be BatchDisplay
+const disp = hp.getDisplay();
+
+for (let id = 0; id < disp.numFrames(); ++id) {
+   const svg = await disp.makeSVG(id);
+   console.log(`Frame ${id} create svg size ${svg.length}`);
+
+   // one can save svg plain file
+   // writeFileSync(`frame${id}.svg`, svg);
+}