add bibtex bibliography file

intro_to_ml.bib

@@ -0,0 +1,32 @@
+@article{huang2006extreme,
+  title={Extreme learning machine: theory and applications},
+  author={Huang, Guang-Bin and Zhu, Qin-Yu and Siew, Chee-Kheong},
+  journal={Neurocomputing},
+  volume={70},
+  number={1-3},
+  pages={489--501},
+  year={2006},
+  publisher={Elsevier}
+}
+
+@article{hastie2020ridge,
+  title={Ridge regularization: an essential concept in data science},
+  author={Hastie, Trevor},
+  journal={Technometrics},
+  volume={62},
+  number={4},
+  pages={426--433},
+  year={2020},
+  publisher={Taylor \& Francis}
+}
+
+@article{rupp2015machine,
+  title={Machine learning for quantum mechanics in a nutshell},
+  author={Rupp, Matthias},
+  journal={International Journal of Quantum Chemistry},
+  volume={115},
+  number={16},
+  pages={1058--1073},
+  year={2015},
+  publisher={Wiley Online Library}
+}