update: add file to mkdocs

mkdocs.yml

@@ -179,6 +179,7 @@ nav:
             - Interface, quick setup (3D Editor):                               tutorials/materials/slabs-interface.md
             - Interface, no strain minimization (Python Transformation):        tutorials/materials/interface-with-python.md
             - Interface, minimal strain (JupyterLite Session):                  tutorials/materials/jupyterlite-zsl.md
+            - Import materials from files:                                      tutorials/materials/import-from-files.md
 
 
 # COMMON UI COMPONENTS