[v2][docs] Improving documentation on side menu config (#3773)

docs/docs/layout-types.md

 
 ## sideMenu
 
-Expect center, left and right layouts
+Expect center, left and right layouts. center: { stack: ... } is required to have a topBar in center screen of a sideMenu app.
 
 ```js
 const sideMenu = {
     component: {}
   },
   center: {
-    stack: {}
+    stack: {
+      options: {},
+      children: [{
+        component: {}
+      }]
+    }
   },
   right: {
     component: {}