Update README.md - Add articles for xgboost (#48)

Author: PetrovKP

README.md

@@ -18,8 +18,10 @@ We publish blogs on Medium, so [follow us](https://medium.com/intel-analytics-so
 - [Improve the Performance of XGBoost and LightGBM Inference](https://medium.com/intel-analytics-software/improving-the-performance-of-xgboost-and-lightgbm-inference-3b542c03447e)
 - [Accelerate Kaggle Challenges Using Intel AI Analytics Toolkit](https://medium.com/intel-analytics-software/accelerate-kaggle-challenges-using-intel-ai-analytics-toolkit-beb148f66d5a)
 - [Accelerate Your scikit-learn Applications](https://medium.com/intel-analytics-software/improving-the-performance-of-xgboost-and-lightgbm-inference-3b542c03447e)
+- [Optimizing XGBoost Training Performance](https://medium.com/intel-analytics-software/new-optimizations-for-cpu-in-xgboost-1-1-81144ea21115)
 - [Accelerate Linear Models for Machine Learning](https://medium.com/intel-analytics-software/accelerating-linear-models-for-machine-learning-5a75ff50a0fe)
 - [Accelerate K-Means Clustering](https://medium.com/intel-analytics-software/accelerate-k-means-clustering-6385088788a1)
+- [Fast Gradient Boosting Tree Inference](https://medium.com/intel-analytics-software/fast-gradient-boosting-tree-inference-for-intel-xeon-processors-35756f174f55)
 
 ## Table of content