updated build link in getting started doc

Author: Stephen Hodgson

GettingStarted.md

@@ -4,7 +4,7 @@ in your project.
 To get started either download the HoloToolkit-Unity Asset Package or grab a copy of this repository and download the entire project.
 
 # 1a. Download a HoloToolkit-Unity Asset Package
-You can download the latest unity package from the [Asset Packages](External/HoloToolkit/AssetPackages/) folder
+You can download the latest unity package from [Releases](https://github.com/Microsoft/HoloToolkit-Unity/releases) folder
 
 [Continue to step 2](/GettingStarted.md#2-using-holotoolkit-unity-in-your-project)