* Added course for Beckhoff's TwinCAT 3.

* Fixed spacing to next heading.

* Update courses/free-courses-en.md

Added platform (YouTube)
Co-authored-by: NDavid Ordás <davorpatech@gmail.com>

* Added additional free courses for TwinCAT 3.
Co-authored-by: NDavid Ordás <davorpatech@gmail.com>