add tip for downloading files

Author: jmckenna

en/mapfile/symbology/construction.txt

@@ -33,6 +33,15 @@ dissertation will also concern this subject.
 
 The document has been heavily revised for MapServer  6.
 
+.. tip::
+
+   All of the mapfiles, symbol files, reports, etc. are still available for download 
+   (you will have to update them for recent MapServer versions, but they are still 
+   very helpful): 1) `mapfiles & symbol files <https://download.osgeo.org/mapserver/docs/vortrag_demo.zip>`__, 
+   2) `research report <https://download.osgeo.org/mapserver/docs/Praktikumsarbeit-2004.pdf>`__ (in German), 
+   and 3) `future improvements <https://download.osgeo.org/mapserver/docs/DiskussionsPaper-UMNGraphikKernel.pdf>`__ (in German).
+
+
 .. _`Download study report`: https://download.osgeo.org/mapserver/docs/Praktikumsarbeit-2004.pdf