Update COMPILING-VS-VCPKG.md to indicate CMake 4 incompatibility (#82831)

Author: akrieger

doc/c++/COMPILING-VS-VCPKG.md

@@ -22,13 +22,13 @@ Steps from current guide were tested on Windows 10 (64 bit), Visual Studio 2019
 
 ## Prerequisites:
 
-* Computer with modern Windows operating system installed (Windows 10, Windows 8.1 or Windows 7);
+* Computer with modern Windows operating system installed (Windows 10, Windows 8.1 or Windows 7 - Windows XP is not supported);
 * NTFS partition with ~15 Gb free space (~10 Gb for Visual Studio, ~1 Gb for vcpkg installation, ~3 Gb for repository and ~1 Gb for build cache);
 * Git for Windows (installer can be downloaded from [Git homepage](https://git-scm.com/));
 * Visual Studio 2019 (or 2015 Visual Studio Update 3 and above);
 * Latest version of vcpkg (see instructions on [vcpkg homepage](https://github.com/Microsoft/vcpkg)).
 
-**Note:** Windows XP is unsupported!
+**WARNING:** If you have CMake 4 or newer installed, you need to downgrade to CMake 3 eg. https://github.com/Kitware/CMake/releases/tag/v3.31.8 or a newer version of CMake 3. CMake 4 is not compatible with the version of vcpkg we use.
 
 ## Installation and configuration: