Update README.md

Author: crazyjackel

README.md

@@ -6,6 +6,8 @@ A Lightweight UniRx Integration into Unity's UI Toolkit.
 ## How to Use
 Follow the Install Instructions for https://github.com/sandolkakos/unity-package-manager-utilities
 
+For Git Versioning and Updates, Install: https://github.com/mob-sakai/UpmGitExtension#usage
+
 Then Just copy the link below and add it to your project via Unity Package Manager: [Installing from a Git URL](https://docs.unity3d.com/Manual/upm-ui-giturl.html)
 ```
 https://github.com/crazyjackel/redmoon-reactiveKit.git