Just started editing

docs/guide/performance.md

 Performance Tuning
 ==================
 
-Application performance consists of two parts. First is the framework performance
+The performance of your web application is based upon two parts. First is the framework performance
 and the second is the application itself. Yii has a pretty low performance impact
 on your application out of the box and can be fine-tuned further for production
 environment. As for the application, we'll provide some of the best practices