Add Redis Books (#6237)

* Add Redis Books

* Ammend PR comment - remove redis for dummies

books/free-programming-books-langs.md

@@ -1583,6 +1583,7 @@ That section got so big, we decided to split it into its own file, the [BY SUBJE
 * [Graph Databases](http://graphdatabases.com)
 * [How To Manage a Redis Database](https://www.digitalocean.com/community/books/how-to-manage-a-redis-database-ebook) - Mark Drake (PDF, EPUB)
 * [NoSQL Databases](http://www.christof-strauch.de/nosqldbs.pdf) - Christof Strauch (PDF)
+* [Redis in Action](https://redis.com/ebook/redis-in-action/) - Josiah L. Carlson
 * [The Little Redis Book](http://openmymind.net/2012/1/23/The-Little-Redis-Book/) - K. Seguin (PDF, Epub)