sample: add sample for "Document:create_processing_instruction()"

Author: komainu8

sample/document-create-processing-instruction.lua

@@ -0,0 +1,16 @@
+#!/usr/bin/env luajit
+
+local xmlua = require("xmlua")
+
+local document = xmlua.XML.build({"root"})
+local processing_instruction =
+  document:create_processing_instruction("xml-stylesheet",
+                                         "href=\"www.test.com/test-style.xsl\" type=\"text/xsl\"")
+local root = document:root()
+root:add_child(processing_instruction)
+print(document:to_xml())
+--<?xml version="1.0" encoding="UTF-8"?>
+--<root>
+--  <?xml-stylesheet href="www.test.com/test-style.xsl" type="text/xsl"?>
+--</root>
+