ICU-21777 Move Windows "ICU4C Platform Support" notes to "Building ICU4C" User Guide...

diff --git a/docs/userguide/icu4c/build.md b/docs/userguide/icu4c/build.md
index 41621b2511ebf4e2c6317ff2f741525c0b916a4c..8e4c76b856a0b77077d7cacc859ab7843edf3beb 100644 (file)
--- a/docs/userguide/icu4c/build.md
+++ b/docs/userguide/icu4c/build.md
@@ -136,9 +136,15 @@ In order to change such user-configurable settings, you can either modify the `u
 
 Building International Components for Unicode requires:
 
-*   Microsoft Windows
-*   Microsoft Visual C++ (part of [Visual Studio](https://www.visualstudio.com/)) (from either Visual Studio 2015 or Visual Studio 2017)
-*   _**Optional:**_ A version of the [Windows 10 SDK](https://developer.microsoft.com/windows/downloads) (if you want to build the UWP projects)
+*   Microsoft Windows 7 or newer. (Windows XP and Windows Vista are not  supported)
+*   Microsoft Visual C++ (part of [Visual Studio](https://www.visualstudio.com/)) (from either Visual Studio 2017 or Visual Studio 2019)
+*   _**Optional:**_ A version of the [Windows 10 SDK](https://developer.microsoft.com/windows/downloads) is needed if you want to build the UWP projects.
+
+Notes regarding Windows specific issues:
+- When using "`@compat=host`" on versions of Windows below Windows 10 version 1703, there are 6 locales with date and number formatting issues ([#13119](https://unicode-org.atlassian.net/browse/ICU-13119)).
+
+- The LCID conversion APIs don't round-trip Kurdish (ku) and Central Kurdish (ckb) due to Windows not having a ckb locale ([#20181](https://unicode-org.atlassian.net/browse/ICU-20181)).
+
 
 > :point_right: **Note**: [Cygwin](#how-to-build-and-install-on-windows-with-cygwin) is required if using a version of MSVC other than the one compatible with the supplied project files or if other compilers are used to build ICU. (e.g. GCC)