added new free course for database management (#4270)

free-courses-en.md

@@ -168,6 +168,7 @@
 * [Database Systems](http://ocw.mit.edu/courses/electrical-engineering-and-computer-science/6-830-database-systems-fall-2010/) (MIT's opencourseware)
 * [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)
 
 
 ### Deep Learning