Update mkdocs.yml

mkdocs.yml

@@ -11,6 +11,7 @@ nav:
   - Vector spaces: '3_vector_spaces.md'
   - Vector spaces in quantum mechanics: '4_vector_spaces_QM.md'
   - Operators in quantum mechanics: '5_operators_QM.md'
+  - Eigenvectors and eigenvalues: '6_eigenvectors_QM.md'
 theme:
   name: material
   custom_dir: theme