docs: added introduction to user guide (#2075)

* docs: added introduction to user guide

* remove link in header

* added UI icons

* small changes

www/docs/sidebars.js

@@ -488,6 +488,13 @@ module.exports = {
       label: "Contribution Guidelines",
     },
   ],
+  userGuideSidebar: [
+    {
+      type: "doc",
+      id: "user-guide/index",
+      label: "Introduction"
+    }
+  ],
   servicesSidebar: [
     {
       type: 'autogenerated',