more intro

content/11-machine-learning/keras-mnist.ipynb

@@ -11,7 +11,9 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "We'll start with a classic exmaple—character recognition"
+    "We’ll apply the ideas we just learned to a neural network that does character recognition using the [MNIST database](https://en.wikipedia.org/wiki/MNIST_database). This is a set of handwritten digits (0–9) represented as a 28×28 pixel grayscale image.\n",
+    "\n",
+    "There are 2 datasets, the training set with 60,000 images and the test set with 10,000 images."
    ]
   },
   {