Add section on build-win32.sh script

README.win32

@@ -1,3 +1,17 @@
+Win32 builds
+------------
+
+MinGW
+=====
+
+For DLLs compatible with MSVC++ cross-compiled from Linux with MinGW, see
+the build-win32.sh script in the scripts/ directory and its companion README
+file.
+
+
+Cygwin
+======
+
 From: "Mark J. Fine" <mark.fine@fineware-swl.com>
 Subject: [Hamlib-developer] Building under Cygwin for Windows (Mingw32)
 List-Archive: <http://sourceforge.net/mailarchive/forum.php?forum=hamlib-developer>