[ReactNative] LayoutAnimation docs

Summary:
Improve https://facebook.github.io/react-native/docs/layoutanimation.html

Libraries/Animation/LayoutAnimation.js

@@ -109,8 +109,32 @@ var Presets = {
   },
 };
 
+/**
+ * Automatically animates views to their new positions when the
+ * next layout happens.
+ *
+ * A common way to use this API is to call `LayoutAnimation.configureNext`
+ * before calling `setState`.
+ */
 var LayoutAnimation = {
+  /**
+   * Schedules an animation to happen on the next layout.
+   *
+   * @param config Specifies animation properties:
+   *
+   *   - `duration` in milliseconds
+   *   - `create`, config for animating in new views (see `Anim` type)
+   *   - `update`, config for animating views that have been updated
+   * (see `Anim` type)
+   *
+   * @param onAnimationDidEnd Called when the animation finished.
+   * Only supported on iOS.
+   * @param onError Called on error. Only supported on iOS.
+   */
   configureNext,
+  /**
+   * Helper for creating a config for `configureNext`.
+   */
   create,
   Types,
   Properties,