* Adding Database Systems free Course

Add youtube video's URL with Database Systems - Cornell University Course (SQL, NoSQL, Large-Scale Data Analysis) subject that created by Professor Immanuel Trummer, PhD and uploaded in the  freeCodeCamp.org youtube channel

* Update courses/free-courses-en.md with better name resources and simpler attributions

Implement the advice about name resources and complex attributions.
Co-authored-by: NDavid Ordás <3125580+davorpa@users.noreply.github.com>
Co-authored-by: NDavid Ordás <3125580+davorpa@users.noreply.github.com>