Add demo for page break before

demo/demo15.js

@@ -0,0 +1,14 @@
+const docx = require('../build');
+
+var doc = new docx.Document();
+
+var paragraph = new docx.Paragraph("Hello World");
+var paragraph2 = new docx.Paragraph("Hello World on another page").pageBreakBefore();
+
+doc.addParagraph(paragraph);
+doc.addParagraph(paragraph2);
+
+var exporter = new docx.LocalPacker(doc);
+exporter.pack('My Document');
+
+console.log('Document created successfully at project root!');