Update free-courses-en.md (#8214)

* Update free-courses-en.md

* Update free-courses-en.md

* Update courses/free-courses-en.md

Co-authored-by: Sharan J <50091666+shrn01@users.noreply.github.com>

* Update free-courses-en.md

Co-authored-by: Sharan J <50091666+shrn01@users.noreply.github.com>

courses/free-courses-en.md

@@ -392,6 +392,7 @@
 
 ### Databases
 
+* [CMU Intro to Database Systems](https://youtube.com/playlist?list=PLSE8ODhjZXjaKScG3l0nuOiDTTqpfnWFf) - CMU Database Group
 * [Database Systems](http://ocw.mit.edu/courses/electrical-engineering-and-computer-science/6-830-database-systems-fall-2010/) (MIT's opencourseware)
 * [Database Systems - Cornell University Course (SQL, NoSQL, Large-Scale Data Analysis)](https://www.youtube.com/watch?v=4cWkVbC2bNE) - Professor Immanuel Trummer, freeCodeCamp.org (YouTube)
 * [DBMS Placement Series](https://youtube.com/playlist?list=PLDzeHZWIZsTpukecmA2p5rhHM14bl2dHU) - CodeHelp by Babbar