Add link to MI-PYT GeoPython materials

Author: hroncok

runs/2017/mipyt-zima/info.yml

@@ -93,7 +93,9 @@ plan:
 - slug: extra
   title: GeoPython (extra workshop)
   date: 2017-12-13
-  materials: []
+  materials:
+  - title: "Externí materiály: Open Source GIS"
+    url: http://training.gismentors.eu/open-source-gis/
 
 - base: async
   date: 2017-12-20