Clarify that wxFileSystem::OpenFile() takes URL, not filename.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@64239 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

interface/wx/filesys.h

@@ -160,6 +160,11 @@ public:
         Passing @e "wxFS_READ | wxFS_SEEKABLE" for @a flags will back
         a stream that is not natively seekable with memory or a file
         and return a stream that is always seekable.
+
+        @note
+        The @a location argument is, despite this method's name @em not
+        a filename. It is a "location", aka wxFileSystem URL (see
+        @ref overview_fs).
     */
     wxFSFile* OpenFile(const wxString& location,
                        int flags = wxFS_READ);