better documented wxListCtrl::GetItem (it was absolutely unclear how to use it)

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@6221 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

docs/latex/wx/listctrl.tex

@@ -258,6 +258,9 @@ Returns the specified image list. {\it which} may be one of:
 Gets information about the item. See \helpref{wxListCtrl::SetItem}{wxlistctrlsetitem} for more
 information.
 
+You must call {\it info.SetId()} to se ID of item you're interested in
+before calling this method.
+
 \pythonnote{The wxPython version of this method takes an integer parameter
 for the item ID, and returns the wxListItem object.
 }