temporarily disable the Fermi surface database

mkdocs.yml

@@ -30,7 +30,7 @@ nav:
   - Summary and review: '15_SummaryAndReview.md'
   - Attic:
     - Magnetism: 'lecture_8.md'
-    - Fermi surface periodic table: 'fermi_surfaces.md'
+    # - Fermi surface periodic table: 'fermi_surfaces.md'
     - Extra exercises: 'extra_exercises.md'
   - Solutions:
     - Einstein model: '1_einstein_model_solutions.md'