add reference tutorial for visualizing layers

neural_style_pytorch/neural_style_tutorial.ipynb

@@ -1028,6 +1028,15 @@
         "        return img_io.getvalue()\n"
       ]
     },
+    {
+      "cell_type": "markdown",
+      "metadata": {},
+      "source": [
+        "https://www.geeksforgeeks.org/visualizing-feature-maps-using-pytorch/\n",
+        "\n",
+        "This tutorial for base to visualize layers"
+      ]
+    },
     {
       "cell_type": "code",
       "execution_count": 28,