doc: update documentation for dialog helper

doc/src/win_import.dox

@@ -4,13 +4,18 @@
 
 Windows is shitty for the programmer who is familiar with UNIX programming.
 Due to legacy reason, Windows defines various things which are not compatible with UNIX or standard C++ programming.
-YYCC has a way to solve this issue.
+
+\section win_import__usage Usage
+
+YYCC has a way to solve the issue introduced above.
 
 \code
+#if YYCC_OS == YYCC_OS_WINDOWS
 #include <WinImportPrefix.hpp>
 #include <Windows.h>
 #include "other_header_depend_on_windows.h"
 #include <WinImportSuffix.hpp>
+#endif
 \endcode
 
 The including of WinImportPrefix.hpp and WinImportSuffix.hpp is a pair.
@@ -43,6 +48,8 @@ This guard can solve following issues:
     </LI>
 </UL>
 
+\section win_import__notes Notes
+
 If you have other header files which are strongly depend on Windows header,
 you should put them into this bracket at the same time like example did.
 Because this guard operate some Windows macros as we introduced above.
@@ -53,4 +60,10 @@ Because they do not have the proprocessor command like <I>#pragma once</I> or et
 That's by design. Because we actually may use this pair multiple times.
 The only thing you should pledge is that you must make sure they are presented by pair.
 
+This guard is Windows specific.
+It does nothing if you accidently use it in other platforms such as Linux,
+because the headers use \c #if to check environment out and will do nothing in non-Windows environment.
+However, we still highly recommend you use this pair with platform checker bracket like example does,
+if your program need to be run on multiple platforms.
+
 */