Merge branch '333-menueintrage' into 'master'

change documentation Overview and technical documentation

Closes #333

See merge request !693

_data/navigation.yml

@@ -49,8 +49,8 @@ header:
         url: "mission"
       - title: "Publications"
         url: "publications"
-      - title: "Technical and Adminstrative Documentation"
-        url: "https://hifis.net/doc"
+      - title: "Documentation Overview"
+        url: "documentation"
       - title: "Partners"
         url: "partners"
       - title: "Who is HIFIS?"
@@ -61,8 +61,9 @@ header:
         entries:
           - title: "Organisational Structure"
             url: "structure"
-          - title: "Documentation Overview"
-            url: "documentation"
+          - title: "Technical and Adminstrative Documentation"
+            url: "https://hifis.net/doc"
+            external: True
           - title: "Reports"
             url: "reports"
           - title: "Surveys"