Add W3Schools' XML tutorial (#7148)

* Update free-programming-books-langs.md

Added course for XML

* move XML section to interactive tutorials

Co-authored-by: David Ordás <3125580+davorpa@users.noreply.github.com>

more/free-programming-interactive-tutorials-en.md

@@ -46,6 +46,7 @@
 * [Selenium](#selenium)
 * [Solidity](#solidity)
 * [SQL](#sql)
+* [XML](#xml)
 
 
 ### Ada
@@ -388,3 +389,8 @@
 * [SQL Tutorial](https://www.w3schools.com/sql) - W3Schools
 * [SQL Tutorial](https://www.scaler.com/topics/sql/) - Scaler Topics
 * [SQLBolt](http://sqlbolt.com)
+
+
+### XML
+
+* [XML Tutorial](https://www.w3schools.com/xml) - W3Schools