Add translation variable for "notes" to base TLs of backend

backend/de/basis.json

@@ -112,6 +112,7 @@
         "annotations": "Anmerkungen",
         "catalogue_raisonne": "Werkverzeichnis",
         "statistics": "Statistik",
-        "analyze": "Analysiere"
+        "analyze": "Analysiere",
+        "notes": "Notizen"
     }
 }