Add Upgrading To The Latest React In CodeSandbox as a react til

README.md

@@ -10,7 +10,7 @@ smart people at [Hashrocket](http://hashrocket.com/).
 For a steady stream of TILs from a variety of rocketeers, checkout
 [til.hashrocket.com](https://til.hashrocket.com/).
 
-_663 TILs and counting..._
+_664 TILs and counting..._
 
 ---
 
@@ -471,6 +471,7 @@ _663 TILs and counting..._
 - [Read Only Input Elements](react/read-only-input-elements.md)
 - [Rendering Multiple Nodes With Fragments](react/rendering-multiple-nodes-with-fragments.md)
 - [Test Files In create-react-app](react/test-files-in-create-react-app.md)
+- [Upgrading To The Latest React In CodeSandbox](react/upgrading-to-the-latest-react-in-codesandbox.md)
 - [Use A Ref To Autofocus An Input](react/use-a-ref-to-autofocus-an-input.md)
 - [Use withRouter To Pass Down React-Router History](react/use-withrouter-to-pass-down-react-router-history.md)
 - [Visually Select A React Element For Inspection](react/visually-select-a-react-element-for-inspection.md)

react/upgrading-to-the-latest-react-in-codesandbox.md

@@ -0,0 +1,12 @@
+# Upgrading To The Latest React In CodeSandbox
+
+At the time of writing this, the latest version of React is 16.3.1. Opening
+up [CodeSandbox](https://codesandbox.io/) and starting a new React project
+has us working with React 16.2.
+
+![Defaults to React 16.2](https://i.imgur.com/AmgyfGc.png)
+
+By clicking on the _circular arrow_ upgrade icon next to `react` and
+`react-dom`, we will have upgraded each to 16.3.1.
+
+![Upgrade to React 16.3.1](https://i.imgur.com/0DPLOY2.png)