Added note about overfitting and the need for model validation in the k-nearest neighbors model.

scikit-learn/scikit-learn-intro.ipynb

@@ -244,6 +244,13 @@
     "from fig_code import plot_iris_knn\n",
     "plot_iris_knn()"
    ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "Note we see overfitting in the K-Nearest Neighbors model above.  We'll be addressing overfitting and model validation in a later notebook."
+   ]
   }
  ],
  "metadata": {