#246 update of documentation lay-out

mkdocs.yml

@@ -82,8 +82,9 @@ nav:
           - "guides/documentation.md"
       - Support:
           - guides/gettinghelp.md
-  - Tutorials:
-      - tutorials/first_steps.ipynb
+  - Tutorials: 
+      - tutorials/tutorials.md
+      - tutorials/build_basic_model.ipynb
       - tutorials/loading_and_saving_a_model.md
       - tutorials/dataframe_handling.md
       - tutorials/plotting_a_network.md