Update free-courses-en.md (#7152)

* Update free-courses-en.md

* Update courses/free-courses-en.md

Co-authored-by: David Ordás <3125580+davorpa@users.noreply.github.com>

Co-authored-by: Peter Morrison <peter.morrison@medlior.com>
Co-authored-by: David Ordás <3125580+davorpa@users.noreply.github.com>

courses/free-courses-en.md

@@ -722,6 +722,7 @@
 * [Intro to Machine Learning Udacity](https://www.udacity.com/course/intro-to-machine-learning--ud120) (Udacity)
 * [Intro to Machine Learning using Microsoft Azure](https://www.udacity.com/course/introduction-to-machine-learning-using-microsoft-azure--ud00333) - Microsoft (Udacity)
 * [Intro to Self-Driving Cars Nanodegree](https://www.udacity.com/course/intro-to-self-driving-cars--nd113) - Cezanne Camacho, Andrew Paster, Anthony Navarro, Tarin Ziyaee, et al. (Udacity)
+* [Introduction to Machine Learning](https://openlearninglibrary.mit.edu/courses/course-v1:MITx+6.036+1T2019/about) - MIT Open Learning Library
 * [Machine Learning](https://www.sololearn.com/Course/machine-learning) (SoloLearn) *(account required)*
 * [Machine Learning Recipes with Josh Gordon](https://www.youtube.com/playlist?list=PLOU2XLYxmsIIuiBfYad6rFYQU_jL2ryal)
 * [Machine Learning Specialization](https://www.coursera.org/specializations/machine-learning-introduction) - Andrew Ng, Eddy Shyu, Aarti Bagul, Geoff Ladwig (Coursera)