Update free-courses-en.md (#3866)

Added python course

free-courses-en.md

@@ -390,6 +390,7 @@
 * [Programming Foundations with Python](https://www.udacity.com/course/programming-foundations-with-python--ud036) (Udacity)
 * [Python Course](http://www.python-course.eu)
 * [Python Programming Tutorial](https://www.youtube.com/playlist?list=PL_RGaFnxSHWpX_byHyTEj9hecPngl2DqR)
+* [SoloLearn](https://www.sololearn.com/Course/Python/)
 
 
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