Added a course in english "CS250: Python for Data Science" from Saylor.org. Please merge. (#7589)

* Added a course in english

* Added a Data Science course in english

* chore: add course platform

* fix: Saylor created a non-profit, he didn't create the course.

Co-authored-by: Eric Hellman <eric@hellman.net>

Co-authored-by: David Ordás <3125580+davorpa@users.noreply.github.com>
Co-authored-by: Eric Hellman <eric@hellman.net>

courses/free-courses-en.md

@@ -328,6 +328,7 @@
 
 * [Advanced Data Mining with Weka MOOC](https://www.cs.waikato.ac.nz/ml/weka/mooc/advanceddataminingwithweka/)
 * [Applied Data Science with Python](https://cognitiveclass.ai/learn/data-science-with-python) - CognitiveClass.ai
+* [CS250: Python for Data Science](https://learn.saylor.org/course/view.php?id=504) - Saylor Academy
 * [Data Analysis and Visualization](https://www.udacity.com/course/data-analysis-and-visualization--ud404) - Georgia Tech (Udacity)
 * [Data Analysis with Python: Zero to Pandas](https://jovian.ai/learn/data-analysis-with-python-zero-to-pandas) (Jovian)
 * [Data Analysis with R](https://www.udacity.com/course/data-analysis-with-r--ud651) - Facebook (Udacity)