docs: add development/testing to links

Author: jescalada

website/sidebars.js

@@ -43,7 +43,7 @@ module.exports = {
       },
       collapsible: true,
       collapsed: false,
-      items: ['development/contributing', 'development/plugins'],
+      items: ['development/contributing', 'development/plugins', 'development/testing'],
     },
   ],
 };