Added comment as to how to execute cells

notebooks/about_this_workshop.ipynb

 {
  "metadata": {
   "name": "",
-  "signature": "sha256:1abbf29ef46d8fc8d1262eca8a9c8da262d15821c04a149ade6e78d73c9b85c5"
+  "signature": "sha256:fc454c5edcc53ce3f39585e61fda6a02b56561debd910c358dc6bc07a394048c"
  },
  "nbformat": 3,
  "nbformat_minor": 0,
@@ -41,22 +41,39 @@
       "Experimenting\n",
       "-----\n",
       "\n",
-      "Code cells are meant to be interactive. If you see a cell like this:"
+      "Code cells are meant to be interactive. If you see a cell like this, you should be able to select it, and from the menu \"Cell\" above, click \"Run\":"
      ]
     },
     {
      "cell_type": "code",
      "collapsed": false,
      "input": [
-      "x = scipy.randn(100)\n",
-      "# x = scipy.rand(100)\n",
-      "# x = scipy.arange(100)\n",
-      "# x = scipy.linspace(0, 1, 100)"
+      "import scipy\n",
+      "\n",
+      "x = scipy.arange(100)\n",
+      "# x = scipy.randn(100)\n",
+      "# x = scipy.linspace(0, 1, 100)\n",
+      "\n",
+      "x"
      ],
      "language": "python",
      "metadata": {},
-     "outputs": [],
-     "prompt_number": 0
+     "outputs": [
+      {
+       "metadata": {},
+       "output_type": "pyout",
+       "prompt_number": 5,
+       "text": [
+        "array([ 0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 12, 13, 14, 15, 16,\n",
+        "       17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33,\n",
+        "       34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50,\n",
+        "       51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67,\n",
+        "       68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84,\n",
+        "       85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99])"
+       ]
+      }
+     ],
+     "prompt_number": 5
     },
     {
      "cell_type": "markdown",