Added some documentation and demo file

demo/66-fields.ts

@@ -0,0 +1,43 @@
+// Use fields to include dynamic text
+// Import from 'docx' rather than '../build' if you install from npm
+import * as fs from "fs";
+import { Bookmark, Document, Packer, Paragraph, SimpleField, TextRun } from "../build";
+
+const doc = new Document({
+    creator: 'Me',
+    sections: [
+        {
+            properties: {},
+            children: [
+                new Paragraph({
+                    children: [
+                        new TextRun("This document is called "),
+                        new SimpleField("FILENAME", "My Document.docx"),
+                        new TextRun(", was created on "),
+                        new SimpleField('CREATEDATE  \\@ "d MMMM yyyy"'),
+                        new TextRun(" by "),
+                        new SimpleField("AUTHOR"),
+                    ],
+                }),
+                new Paragraph({
+                    children: [
+                        new TextRun("The document has "),
+                        new SimpleField("NUMWORDS", "34"),
+                        new TextRun(" words and if you'd print it "),
+                        new Bookmark({
+                            id: "TimesPrinted",
+                            children: [new TextRun("42")],
+                        }),
+                        new TextRun(" times two-sided, you would need "),
+                        new SimpleField("=INT((TimesPrinted+1)/2)"),
+                        new TextRun(" sheets of paper."),
+                    ],
+                }),
+            ],
+        },
+    ],
+});
+
+Packer.toBuffer(doc).then((buffer) => {
+    fs.writeFileSync("My Document.docx", buffer);
+});