Make .addSection fully declarative

demo/56-background-color.ts

@@ -7,24 +7,25 @@ const doc = new Document({
     background: {
         color: "C45911",
     },
-});
-
-doc.addSection({
-    properties: {},
-    children: [
-        new Paragraph({
+    sections: [
+        {
+            properties: {},
             children: [
-                new TextRun("Hello World"),
-                new TextRun({
-                    text: "Foo Bar",
-                    bold: true,
-                }),
-                new TextRun({
-                    text: "\tGithub is the best",
-                    bold: true,
+                new Paragraph({
+                    children: [
+                        new TextRun("Hello World"),
+                        new TextRun({
+                            text: "Foo Bar",
+                            bold: true,
+                        }),
+                        new TextRun({
+                            text: "\tGithub is the best",
+                            bold: true,
+                        }),
+                    ],
                 }),
             ],
-        }),
+        },
     ],
 });