added a note about entry point in Unicode build (patch 1934836)

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_2_8_BRANCH@53058 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

samples/mfc/mfctest.cpp

@@ -40,6 +40,10 @@
 //
 //     Unless the run-time library settings match for wxWidgets and MFC, you will get
 //     link errors for symbols such as __mbctype, __argc, and __argv 
+//
+// (3) Unicode builds may produce the linker error "unresolved external symbol _WinMain@16".
+//     MFC requires you to manually add the Unicode entry point to the linker settings,
+//     Entry point symbol -> wWinMainCRTStartup
 
 #include "stdafx.h"