Added import statement to section 1

Author: Christopher Fonnesbeck

1. Introduction to Pandas.ipynb

@@ -53,6 +53,7 @@
      "collapsed": false,
      "input": [
       "import pandas as pd\n",
+      "import numpy as np\n",
       "\n",
       "# Set some Pandas options\n",
       "pd.set_option('html', False)\n",