Update "optimizing performance" instructions for React 16 (#356)

content/docs/optimizing-performance.md

@@ -164,7 +164,7 @@ In the **development** mode, you can visualize how components mount, update, and
 
 To do this in Chrome:
 
-1. Load your app with `?react_perf` in the query string (for example, `http://localhost:3000/?react_perf`).
+1. Make sure you're running the application in the development mode.
 
 2. Open the Chrome DevTools **[Performance](https://developers.google.com/web/tools/chrome-devtools/evaluate-performance/timeline-tool)** tab and press **Record**.
 
@@ -174,11 +174,12 @@ To do this in Chrome:
 
 5. React events will be grouped under the **User Timing** label.
 
+For a more detailed walkthrough, check out [this article by Ben Schwarz](https://building.calibreapp.com/debugging-react-performance-with-react-16-and-chrome-devtools-c90698a522ad).
+
 Note that **the numbers are relative so components will render faster in production**. Still, this should help you realize when unrelated UI gets updated by mistake, and how deep and how often your UI updates occur.
 
 Currently Chrome, Edge, and IE are the only browsers supporting this feature, but we use the standard [User Timing API](https://developer.mozilla.org/en-US/docs/Web/API/User_Timing_API) so we expect more browsers to add support for it.
 
-
 ## Avoid Reconciliation
 
 React builds and maintains an internal representation of the rendered UI. It includes the React elements you return from your components. This representation lets React avoid creating DOM nodes and accessing existing ones beyond necessity, as that can be slower than operations on JavaScript objects. Sometimes it is referred to as a "virtual DOM", but it works the same way on React Native.