Added DBMS Course (#7542)

* Added DBMS Course

* Update free-courses-en.md

* Update free-courses-en.md

* Update courses/free-courses-en.md

Co-authored-by: Eric Hellman <eric@hellman.net>

Co-authored-by: Eric Hellman <eric@hellman.net>

courses/free-courses-en.md

@@ -345,6 +345,7 @@
 
 * [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
 * [DML Server Administration](https://alison.com/course/databases-dml-statements-and-sql-server-administration-revised) (Alison)
 * [Introduction to Databases](https://lagunita.stanford.edu/courses/Engineering/db/2014_1/about) (Stanford University)
 * [Learn SQL Basic for Data Science Specialisation](https://www.coursera.org/specializations/learn-sql-basics-data-science#about) (Coursera)