Dev #8: Explicitly state extension for numpy files

notebook.ipynb

@@ -1216,7 +1216,7 @@
     "└── 2020_04_02.npy\n",
     "```\n",
     "\n",
-    "The persistence and respective use of these results is then up to the user. They consist of numpy files for each test date that contain the following:\n",
+    "The persistence and respective use of these results is then up to the user. They consist of NumPy (*.npy) files for each test date that contain the following:\n",
     "1. *forecast*: The neural network predicted forecast sea ice concentration data.\n",
     "1. *outputs*: Outputs from the data loader used for training.\n",
     "1. *sample_weights*: The sample weights used to weight training samples.\n",