Made demo files into typescript files

demo/demo8.ts

@@ -0,0 +1,17 @@
+// Add text to header and footer
+// Import from 'docx' rather than '../build' if you install from npm
+import * as fs from "fs";
+import { Document, Packer } from "../build";
+
+const doc = new Document();
+
+doc.createParagraph("Hello World");
+
+doc.Header.createParagraph("Header text");
+doc.Footer.createParagraph("Footer text");
+
+const packer = new Packer();
+
+packer.toBuffer(doc).then((buffer) => {
+    fs.writeFileSync("My Document.docx", buffer);
+});