Mention that wxNotebook page must be removed before reparenting it.

At least in wxGTK it is necessary to remove the page from the notebook first
as reparenting it doesn't work otherwise currently.

This should ideally be fixed but in the meanwhile at least document it.

See #13305.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@68214 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

interface/wx/window.h

@@ -495,6 +495,9 @@ public:
         current parent window (e.g. a non-standard toolbar in a wxFrame)
         and then re-inserted into another.
 
+        Notice that currently you need to explicitly call
+        wxNotebook::RemovePage() before reparenting a notebook page.
+
         @param newParent
             New parent.
     */