add documentation about JS library usage. fixes #733

Summary: Adds an example of how to use yoga from JavaScript to the documentation pages.

Reviewed By: priteshrnandgaonkar

Differential Revision: D7354390

fbshipit-source-id: 0dbc08e5341c06b621acd99bfb9ce7e789b67a45

website/contents/getting-started/standalone.md

@@ -18,10 +18,45 @@ dependencies {
 
 ### Javascript
 
+The JavaScript bindings for Yoga can be used from node.js and within the browser.
+When using Yoga from node.js the native library is used, in browesers a pure JS
+version is used (corss-compiled using [emscripten](http://kripken.github.io/emscripten-site/)).
+
 ```
 $> yarn add yoga-layout
 ```
 
+This is an example on how to use Yoga in JavaScript, for a full API reference,
+have a look at the [flow-type definitions](https://github.com/facebook/yoga/blob/master/javascript/sources/entry-common.js#L123).
+
+```js
+import yoga, {Node} from 'yoga-layout';
+
+const root = Node.create();
+root.setWidth(500);
+root.setHeight(300);
+root.setJustifyContent(yoga.JUSTIFY_CENTER);
+
+const node1 = Node.create();
+node1.setWidth(100);
+node1.setHeight(100);
+
+const node2 = Node.create();
+node2.setWidth(100);
+node2.setHeight(100);
+
+root.insertChild(node1, 0);
+root.insertChild(node2, 1);
+
+root.calculateLayout(500, 300, yoga.DIRECTION_LTR);
+console.log(root.getComputedLayout());
+// {left: 0, top: 0, width: 500, height: 300}
+console.log(node1.getComputedLayout());
+// {left: 150, top: 0, width: 100, height: 100}
+console.log(node2.getComputedLayout());
+// {left: 250, top: 0, width: 100, height: 100}
+```
+
 ### iOS
 
 ```