updated branch (#6671)

* Update free-courses-en.md

Added free courses with their link for machine learning and data science.

* Update free-courses-en.md

Added free courses for data science and machine learning with correct alphabetical order.

* Update free-courses-en.md

Added free course for machine learning in alphabetical order.

* Update free-courses-en.md

* Update free-courses-en.md

Author: kartikay23