fix: fix typo in tutorial

docs/examples/Tutorial_10b_Custom_Coating_Types.ipynb

@@ -287,7 +287,7 @@
     "- This tutorial showed how to add custom coatings to surfaces in Optiland.\n",
     "- Creating a custom coating only requires you inherit from BaseCoating, then define the reflect and transmit methods.\n",
     "- We created a simple gradient coating and a spectrally-resolved coating.\n",
-    "- More advanced coating can be made that are dependent on the ray properties, or surface normals."
+    "- More advanced coatings can be made that are dependent on the ray properties, or surface normals."
    ]
   }
  ],