Add Playfair's original graph

module3/exo3/exercice.ipynb

@@ -533,6 +533,14 @@
     "ax2.set_ylabel('Price of a quarter of wheat (Shillings)')\n"
    ]
   },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "**And comparing with the [original graph](https://upload.wikimedia.org/wikipedia/commons/3/3a/Chart_Showing_at_One_View_the_Price_of_the_Quarter_of_Wheat%2C_and_Wages_of_Labour_by_the_Week%2C_from_1565_to_1821.png):**\n",
+    "![original graph](https://upload.wikimedia.org/wikipedia/commons/3/3a/Chart_Showing_at_One_View_the_Price_of_the_Quarter_of_Wheat%2C_and_Wages_of_Labour_by_the_Week%2C_from_1565_to_1821.png)"
+   ]
+  },
   {
    "cell_type": "markdown",
    "metadata": {},