docs: add worker mode documentation + improvements (#11812)

www/apps/book/sidebar.mjs

@@ -605,6 +605,11 @@ export const sidebars = [
             path: "/learn/build",
             title: "Build",
           },
+          {
+            type: "link",
+            path: "/learn/production/worker-mode",
+            title: "Worker Mode",
+          },
           {
             type: "link",
             path: "/learn/deployment",