Add custom properties demo

demo/54-custom-properties.ts

@@ -0,0 +1,25 @@
+// Custom Properties
+// Custom properties are incredibly useful if you want to be able to apply quick parts or custom cover pages
+// to the document in Word after the document has been generated. Standard properties (such as creator, title
+// and subject) cover typical use cases, but sometimes custom properties are required.
+
+// 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(
+    // Standard properties
+    { creator: "Creator", title: "Title", subject: "Subject", description: "Description" },
+    // No file properties
+    {},
+    // No sections
+    [],
+    [
+        { name: "Subtitle", value: "Subtitle" },
+        { name: "Address", value: "Address" },
+    ]
+);
+
+Packer.toBuffer(doc).then((buffer) => {
+    fs.writeFileSync("My Document.docx", buffer);
+});