Add layout direction documentation (#1599)

Summary:
Pull Request resolved: https://github.com/facebook/yoga/pull/1599

tsia. Had to add JS api support for set/get direction

Reviewed By: yungsters

Differential Revision: D54778992

fbshipit-source-id: 346152e1d61c80aa524b515e8b30a96fe32fe7c3

website-next/docs/examples/layout-direction.mdx

@@ -2,4 +2,33 @@
 sidebar_position: 10
 ---
 
+import Playground from '@site/src/components/Playground';
+
 # Layout Direction
+
+Layout direction specifies the direction in which children and text
+in a hierarchy should be laid out. Layout direction also effects what
+edge `start` and `end` refer to. By default Yoga lays out with `LTR`
+layout direction. In this mode `start` refers to `left` and `end`
+refers to `right`. When localizing your apps for markets with RTL languages
+you should customize this by either by passing a direction
+to the `CalculateLayout` call or by setting the direction on the root node.
+
+**LTR (default)**: Text and children and laid out from left to right. Styles applied
+the start of an element are applied on the left side.
+
+**RTL**: Text and children and laid out from right to left. Styles applied the
+start of an element are applied on the right side.
+
+<Playground code={`<Layout config={{useWebDefaults: false}}>
+  <Node
+    style={{
+      width: 200,
+      height: 200,
+      padding: 10,
+      direction: 'ltr'
+    }}>
+    <Node style={{margin: 5, height: 50, width: 50}} />
+    <Node style={{margin: 5, height: 50, width: 50}} />
+  </Node>
+</Layout>`} />