docs: added directory structure documentation (#4612)

* docs: added directory structure documentation

* improvements

www/docs/sidebars.js

@@ -1157,6 +1157,11 @@ module.exports = {
         sidebar_is_group_headline: true,
       },
       items: [
+        {
+          type: "doc",
+          id: "development/backend/prepare-environment",
+          label: "Prepare Environment",
+        },
         {
           type: "doc",
           id: "development/backend/install",
@@ -1164,8 +1169,8 @@ module.exports = {
         },
         {
           type: "doc",
-          id: "development/backend/prepare-environment",
-          label: "Prepare Environment",
+          id: "development/backend/directory-structure",
+          label: "Directory Structure",
         },
         {
           type: "doc",