Added Gradient Boosting Parameter Tuning example from AV

Author: rishabh-joshi

scikit-learn/9. ensemble_methods.ipynb

@@ -324,7 +324,9 @@
     "\n",
     "## Gradient Tree Boosting\n",
     "\n",
-    "[GradientBoostingClassifier](http://scikit-learn.org/stable/modules/generated/sklearn.ensemble.GradientBoostingClassifier.html#sklearn.ensemble.GradientBoostingClassifier) for classification and [GradientBoostingRegressor](http://scikit-learn.org/stable/modules/generated/sklearn.ensemble.GradientBoostingRegressor.html#sklearn.ensemble.GradientBoostingRegressor) for regression.\n",
+    "[GradientBoostingClassifier](http://scikit-learn.org/stable/modules/generated/sklearn.ensemble.GradientBoostingClassifier.html#sklearn.ensemble.GradientBoostingClassifier) for classification and [GradientBoostingRegressor](http://scikit-learn.org/stable/modules/generated/sklearn.ensemble.GradientBoostingRegressor.html#sklearn.ensemble.GradientBoostingRegressor) for regression. \n",
+    "\n",
+    "A very useful [example](https://www.analyticsvidhya.com/blog/2016/02/complete-guide-parameter-tuning-gradient-boosting-gbm-python/) regarding parameter tuning in Gradient Boosting.\n",
     "\n",
     "### Classification example"
    ]