Doc updates for React 16 + blog post (#10824)

* Doc updates for React 16 + blog post

* Add link to Sophie's post

docs/reference-javascript-environment-requirements.md

@@ -0,0 +1,32 @@
+---
+id: javascript-environment-requirements
+title: JavaScript Environment Requirements
+layout: docs
+category: Reference
+permalink: docs/javascript-environment-requirements.html
+---
+
+React 16 depends on the collection types [Map](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map) and [Set](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set). If you support older browsers and devices which may not yet provide these natively (e.g. IE < 11), consider including a global polyfill in your bundled application, such as [core-js](https://github.com/zloirock/core-js) or [babel-polyfill](https://babeljs.io/docs/usage/polyfill/).
+
+A polyfilled environment for React 16 using core-js to support older browsers might look like:
+
+```js
+import 'core-js/es6/map';
+import 'core-js/es6/set';
+
+import React from 'react';
+import ReactDOM from 'react-dom';
+
+ReactDOM.render(
+  <h1>Hello, world!</h1>,
+  document.getElementById('root')
+);
+```
+
+React also depends on `requestAnimationFrame` (even in test environments). A simple shim for testing environments would be:
+
+```js
+global.requestAnimationFrame = function(callback) {
+  setTimeout(callback, 0);
+};
+```