Add free-programming-interactive-tutorials-en for Redis (#3847)

* Added Redis interactive tutorial

* updated docs location

free-programming-playgrounds.md

@@ -23,6 +23,7 @@
 * [Python](#python)
 * [R](#r)
 * [React](#react)
+* [Redis](#redis)
 * [Ruby](#ruby)
 * [Rust](#rust)
 * [RxJS](#rxjs)
@@ -165,6 +166,11 @@
 * [StackBlitz](https://stackblitz.com/fork/react)
 
 
+### Redis
+
+* [Try Redis](https://try.redis.io)
+
+
 ### Ruby
 
 * [Codepad](http://codepad.org)