Add SQLBolt

free-programming-interactive-tutorials-en.md

@@ -25,6 +25,7 @@
 * [R](#r)
 * [Ruby](#ruby)
 * [Scala](#scala)
+* [SQL](#sql)
 * [Vim](#vim)
 
 
@@ -168,5 +169,9 @@
 * [Scala Tour](http://www.scala-tour.com/)
 
 
+### SQL
+* [SQLBolt](http://sqlbolt.com/)
+
+
 ### Vim
 * [Interactive Vim Tutorial](http://www.openvim.com/tutorial.html)