docs: added a how-to guide for customer groups (#2362)

* docs: added how-to guide for customer groups

* added link to new documentation

www/docs/sidebars.js

@@ -222,12 +222,18 @@ module.exports = {
             },
             {
               type: "doc",
-              id: "advanced/backend/price-lists/use-api"
+              id: "advanced/backend/price-lists/use-api",
+              label: "Use PriceList APIs"
             },
             {
               type: "doc",
               id: "advanced/backend/sales-channels/manage-admin",
-              label: "Manage Sales Channels"
+              label: "Use SalesChannel APIs"
+            },
+            {
+              type: "doc",
+              id: "advanced/admin/use-customergroups-api",
+              label: "Use CustomerGroup APIs"
             },
           ]
         },