Update batch generator input dimensions in user guide notebook for improved performance

Author: andersy005

doc/user-guide/training-a-neural-network-with-Pytorch-and-xbatcher.ipynb

@@ -85,9 +85,9 @@
    "source": [
     "# Define batch generators\n",
     "X_bgen = xb.BatchGenerator(\n",
-    "    ds['images'], input_dims={'sample': 2000, 'channel': 1, 'height': 28, 'width': 28}\n",
+    "    ds['images'], input_dims={'sample': 3000, 'channel': 1, 'height': 28, 'width': 28}\n",
     ")\n",
-    "y_bgen = xb.BatchGenerator(ds['labels'], input_dims={'sample': 2000})\n",
+    "y_bgen = xb.BatchGenerator(ds['labels'], input_dims={'sample': 3000})\n",
     "X_bgen[0]"
    ]
   },