Added upgrade guide to Readme

Author: StephenHodgson

README.md

@@ -18,6 +18,8 @@ Learn more about [mixed reality](https://developer.microsoft.com/en-us/windows/m
 [unity-version-badge]:            https://img.shields.io/badge/current%20unity%20editor%20version-2017.1.2f1-green.svg
 [![Github Release][unity-version-badge]][unity-download]
 
+Looking to upgrade your projects to Windows Mixed Reality? [Follow the Upgrade Guide](/UpgradeGuide.md).
+
 # Feature areas
 | ![Input](External/ReadMeImages/MRTK170802_Short_03.png) [Input](Assets/HoloToolkit/Input/README.md)| ![Sharing](External/ReadMeImages/MRTK170802_Short_04.png) [Sharing](Assets/HoloToolkit/Sharing/README.md)| ![Spatial Mapping](External/ReadMeImages/MRTK170802_Short_05.png) [Spatial Mapping](Assets/HoloToolkit/SpatialMapping/README.md)| ![Spatial Understanding](External/ReadMeImages/MRTK170802_Short_06.png) [Spatial Understanding](Assets/HoloToolkit/SpatialUnderstanding/README.md)|
 | :--------------------- | :----------------- | :------------------ | :------------------------ |