[unity] Added changelog entry of last commit (outline at shaders) to 3.9 section as well.

CHANGELOG.md

@@ -53,6 +53,8 @@
   * **Additional Timeline features.** SpineAnimationStateClip now provides a `Speed Multiplier`, a start time offset parameter `Clip In`, support for blending successive animations by overlapping tracks. An additional `Use Blend Duration` parameter *(defaults to true)* allows for automatic synchronisation of MixDuration with the current overlap blend duration. An additional Spine preferences parameter `Use Blend Duration` has been added which can be disabled to default to the previous behaviour before this update.
   * Additional `SpriteMask and RectMask2D` example scene added for demonstration of mask setup and interaction.
   * `Real physics hinge chains` for both 2D and 3D physics. The [SkeletonUtilityBone](http://esotericsoftware.com/spine-unity#SkeletonUtilityBone) Inspector provides an interface to create 2D and 3D hinge chains. Previously created chains have only been respecting gravity, but not momentum of the skeleton or parent bones. The new physics rig created when pressing `Create 3D Hinge Chain` and `Create 2D Hinge Chain` creates a more complex setup that also works when flipping the skeleton. Note that the chain root node is no longer parented to bones of the skeleton. This is a requirement in Unity to have momentum applied properly - do not reparent the chain root to bones of your skeleton, or you will loose any momentum applied by the skeleton's movement.
+  * `Outline rendering functionality for all shaders.` Every shader now provides an additional set of `Outline` parameters to enable custom outline rendering. When outline rendering is enabled via the `Material` inspector, it automatically switches the shader to the respective `Spine/Outline` shader variant. Outlines are generated by sampling neighbour pixels, so be sure to add enough transparent padding when exporting your atlas textures to fit the desired outline width. In order to enable outline rendering at a skeleton, it is recommended to first prepare an additional outline material copy and then switch the material of the target skeleton to this material. This prevents unnecessary additional runtime material copies and drawcalls. Material switching can be prepared via a [SkeletonRendererCustomMaterials](http://esotericsoftware.com/spine-unity#SkeletonRendererCustomMaterials) component and then enabled or disabled at runtime. Alternatively, you can also directly modify the `SkeletonRenderer.CustomMaterialOverride` property.
+  Outline rendering is fully supported on `SkeletonGraphic` shaders as well.
 
 
 * **Changes of default values**