Document wxWindow::FindWindow() TLW skipping behaviour.

Explicitly mention that TLW "children" are not searched by this function
(which is the case since r74721).

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@75608 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

interface/wx/window.h

@@ -455,13 +455,21 @@ public:
 
     /**
         Find a child of this window, by @a id.
+
         May return @a this if it matches itself.
+
+        Notice that only real children, not top level windows using this window
+        as parent, are searched by this function.
     */
     wxWindow* FindWindow(long id) const;
 
     /**
         Find a child of this window, by name.
+
         May return @a this if it matches itself.
+
+        Notice that only real children, not top level windows using this window
+        as parent, are searched by this function.
     */
     wxWindow* FindWindow(const wxString& name) const;