Update README.md

spine-tk2d/README.md

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 The spine-tk2d runtime provides functionality to load, manipulate and render [Spine](http://esotericsoftware.com) skeletal animation data using [2D Toolkit](http://www.unikronsoftware.com/2dtoolkit/) for [Unity](http://unity3d.com/). spine-tk2d is based on [spine-csharp](https://github.com/EsotericSoftware/spine-runtimes/tree/master/spine-csharp) and is very similar to [spine-unity](https://github.com/EsotericSoftware/spine-runtimes/tree/master/spine-unity).
 
+A Spine skeleton is a single GameObject and can be used throughout Unity like any other GameObject. The `BoneComponent` class allows other GameObjects to follow a bone in a Spine skeleton.
+
 ## Setup
 
 1. Download the Spine Runtimes source using [git](https://help.github.com/articles/set-up-git) or by downloading it [as a zip](https://github.com/EsotericSoftware/spine-runtimes/archive/master.zip).
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 # Notes
 
-- Atlas images must use premultiplied alpha.
-- This slightly outdated [setup tutorial video](http://www.youtube.com/watch?v=dnQbS9ap-i8) may still be useful to some.
+- Atlas images should use premultiplied alpha when using the shaders that come with spine-tk2d.
+- This slightly outdated [spine-tk2d setup video](http://www.youtube.com/watch?v=dnQbS9ap-i8) may still be useful.