Update Readme file with C++ modules info

Author: fdwr

README.md

@@ -6,6 +6,9 @@ Supports:
 - DirectWrite, Direct2D, GDI, GDI+
 - Requires Windows 7+. Certain features like Direct2D SVG rendering requires Windows 10 RS4.
 
-C++, compiled with Visual Studio Professional 2017 Version 15.6.5 (Community Edition should work too).
-
+C++, compiled with Visual Studio Professional 2019 16.5.4 (Community Edition should work too).
+Note the project now uses C++ modules.
+To use normal header files, USE_CPP_MODULES=0 in the project properties preprocessor definitions.
+This will also let you use VS 2017 Version 15.6.5 (the compiler crashed when trying to use modules).
+             
 ![Image of TextLayoutSampler](TextLayoutSampler.png)