Document wxHSCROLL and wxVSCROLL styles for wxScrolled<>.

Explain that by default both styles are assumed but that using just one of
them disables the scrolling in the other direction.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@72620 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

interface/wx/scrolwin.h

@@ -99,6 +99,16 @@ enum wxScrollbarVisibility
     of (10,-90).
 
     @beginStyleTable
+    @style{wxHSCROLL}
+           If this style is specified and ::wxVSCROLL isn't, the window will be
+           scrollable only in horizontal direction (by default, i.e. if neither
+           this style nor ::wxVSCROLL is specified, it scrolls in both
+           directions).
+    @style{wxVSCROLL}
+           If this style is specified and ::wxHSCROLL isn't, the window will be
+           scrollable only in vertical direction (by default, i.e. if neither
+           this style nor ::wxHSCROLL is specified, it scrolls in both
+           directions).
     @style{wxRETAINED}
            Uses a backing pixmap to speed refreshes. Motif only.
     @endStyleTable