Clarify that Windows 11 is required to build (microsoft#1893)

Author: mcooley

README.md

@@ -22,7 +22,7 @@ Calculator ships regularly with new features and bug fixes. You can get the late
 
 ## Getting started
 Prerequisites:
-- Your computer must be running Windows 10, version 1809 or newer. Windows 11 is recommended.
+- Your computer must be running Windows 11, build 22000 or newer.
 - Install the latest version of [Visual Studio](https://developer.microsoft.com/en-us/windows/downloads) (the free community edition is sufficient).
   - Install the "Universal Windows Platform Development" workload.
   - Install the optional "C++ Universal Windows Platform tools" component.