Change docx folder to more appropriate "file" folder

src/file/document/body/doc-grid.ts

@@ -0,0 +1,11 @@
+import { Attributes, XmlComponent } from "../../xml-components";
+
+export class DocumentGrid extends XmlComponent {
+
+    constructor() {
+        super("w:docGrid");
+        this.root.push(new Attributes({
+            linePitch: "360",
+        }));
+    }
+}