documented option enabling DirectDraw implementation of wxDisplay under MSW

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@38148 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

docs/latex/wx/sysopt.tex

@@ -28,6 +28,9 @@ pages).}
 \twocolitem{msw.staticbox.optimized-paint}{If set to 0, switches off optimized wxStaticBox painting.
 Setting this to 0 causes more flicker, but allows applications to paint graphics on the parent of a static box
 (the optimized refresh causes any such drawing to disappear).}
+\twocolitem{msw.display.directdraw}{If set to 1, use DirectDraw-based implementation of
+\helpref{wxDisplay}{wxdisplay}. By default the standard Win32 functions are
+used.}
 \end{twocollist}
 
 \wxheading{Mac}