Add android docs

Summary: Adds docs for how to build the Android sample app and use the `YogaLayout`.

Reviewed By: emilsjolander

Differential Revision: D4557955

fbshipit-source-id: 49a3b8fde20de81a895244ffcecbd5bf392455b0

docs/_data/nav_docs.yml

@@ -21,5 +21,6 @@
   - id: c
   - id: yogakit
   - id: java
+  - id: android
   - id: csharp
   - id: javascript

docs/_docs/api/android.md

@@ -0,0 +1,28 @@
+---
+docid: android
+title: Android
+layout: docs
+permalink: /docs/api/android/
+---
+
+There is an easy interface to Yoga called `YogaLayout`.  This is a view group that lays out its children using Yoga.  We recommend looking at the sample app for details on its usage.  However, as an overview you can simply define XML layouts such as
+
+<script src="https://gist.github.com/rspencer01/c1964b98f0c60de7c49683a049ed0640.js"></script>
+
+Note that there are some caveats, such as requiring the custom `YogaLayoutViewFactory` in order to have tags `YogaLayout` instead of `com.facebook.samples.yoga.YogaLayout`.
+
+## layout\_width and layout\_height
+
+If either are set to an actual size (in px or dp etc) then this is taken as a default for `yoga:height` or `yoga:width`.  Otherwise they are ignored.
+
+## VirtualYogaLayout
+
+Sometimes you will nest `YogaLayout`s within `YogaLayout`s in order to get your layout to be perfect, but some of the `YogaLayout`s are just there to control position: they don't render or anything.  If so, then they are unnecessary (since Yoga stores the view hierarchy itself) and `VirtualYogaLayout` is a ViewGroup that fixes this.  It will never get drawn, but all its children will be placed appropriately.
+
+## RTL locales
+
+RTL locales are supported by default.  That is, unless you explicitly set the `yoga:direction="ltr|rtl|inherit"` attribute on a view, it will obtain the locale direction _at runtime_.  This means that the layout will rearrange properly, even if the locale changes while your app is running!
+
+## Attributes
+
+The list of all attributes can be found in [attrs.xml](https://github.com/facebook/yoga/blob/master/android/sample/res/com/facebook/samples/yoga/res/values/attrs.xml), but logically map from the Yoga properties.

docs/_docs/getting-started.md

@@ -13,12 +13,22 @@ Installation of Yoga is currently a manual process. We have plans on bringing Yo
 
 For now we recommend including Yoga as a [git submodule](https://git-scm.com/docs/git-submodule) in your project. Once done, you can either build Yoga using Buck (detailed [below](#building-with-buck)) or integrate it into your existing build system by including the C library from the [root `yoga` directory](https://github.com/facebook/yoga/tree/master/yoga) as well as the [language bindings](https://github.com/facebook/yoga) (e.g., Java, C#) you wish to use.
 
-### Running the Example
+### Running the Examples
+
+#### iOS
 
 Yoga ships with an [iOS example](https://github.com/facebook/yoga/tree/master/YogaKit/YogaKitSample). To get it running:
 
 <script src="https://gist.github.com/emilsjolander/903b16185b24c957acc4cd250c6e73d9.js"></script>
 
+#### Android
+
+Yoga ships with an [Android example too](https://github.com/facebook/yoga/tree/master/android/sample). To get it running on an attached device (or emulator):
+
+<script src="https://gist.github.com/rspencer01/a512f7cd24055c948675be15d48eba78.js"></script>
+
+Actually, this is more than just an example, and more a layout system for Android using Yoga in general (see `YogaLayout`).  For more information see the [Android API section](/yoga/docs/api/android).
+
 ### Building with Buck
 
 Yoga uses [Buck](https://buckbuild.com/) as its build system. Buck is not required for using Yoga, but, if you already use Buck, then integrating Yoga is very simple.