Update free-courses-en.md (#7326)

* Update free-courses-en.md

* fix title

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

courses/free-courses-en.md

@@ -725,6 +725,7 @@
 * [Programming in Java](https://nptel.ac.in/courses/106/105/106105191/) - Prof. Debasis Samanta (NPTEL)
 * [Software Construction in Java](https://openlearninglibrary.mit.edu/courses/course-v1:MITx+6.005.1x+3T2016/about) - MIT Open Learning Library
 * [Spring 5 Core - An Ultimate Guide](https://www.udemy.com/learn-spring-5-core-from-scratch/) - Somnath Musib (Udemy)
+* [What is Java?](https://sagecode.net/java/index.html) - Elucian Moise (Sage-Code)
 
 
 ### JavaScript