Add information for building modbus.dll with Visual Studio 2005

Thank you Petr Gladkiy

src/win32/README.win32

@@ -16,3 +16,5 @@ or
 or
    double click configure.js to generate these files.
 
+To get project file for Visual Studio 2005 open copy of file modbus.vcproj in
+editor and change attribute `Version` of `VisualStudioProject` tag to "8,00".