Added link to Economist 50 shades pic

Author: arnicas

4. Naive Bayes Classification.ipynb

@@ -1,7 +1,7 @@
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-  "signature": "sha256:f5ef3932f292ad28550cc4e674cbafab5a06a4819b359c98ae2bd19888a50358"
+  "signature": "sha256:f0e926c40954923308721ad65f8a417829292d4ba66a385c38c7d0d1ca29dfd1"
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@@ -33,7 +33,7 @@
      "metadata": {},
      "source": [
       "\n",
-      "Inspired by this image from the Economist:\n",
+      "Inspired by this image from the Economist (orignally http://www.economist.com/blogs/graphicdetail/2012/11/fifty-shades-data-visualisations):\n",
       "<img src=\"images/econ_fifty_book1.png\">\n",
       "\n",
       "   \n",