Update machine-learning.md

Author: clarecorthell

machine-learning.md

@@ -5,6 +5,9 @@
  * def: [```scikit / tf-idf```](http://stackoverflow.com/questions/8897593/similarity-between-two-text-documents)
 * [Vectorization and Features in sci-kit (ipynb)](http://nbviewer.ipython.org/github/bigsnarfdude/machineLearning/blob/master/Vectorizing.ipynb)
 
+### Regression
+* [Linear Regression](http://alexhwoods.com/2015/07/19/guide-to-linear-regression/)
+
 ### Models & Methods
 
 * [cosine similarity for vector space models](http://pyevolve.sourceforge.net/wordpress/?p=2497)