Add new MongoDB book at free-programming-books-langs.md

Added MongoDB Notes for Professionals

books/free-programming-books-langs.md

@@ -1509,6 +1509,7 @@ That section got so big, we decided to split it into its own file, the [BY SUBJE
 * [Graph Databases](http://graphdatabases.com)
 * [Introduction to MongoDB](https://www.tutorialspoint.com/mongodb) - Tutorials Point
 * [MongoDB Koans](https://github.com/chicagoruby/MongoDB_Koans)
+* [MongoDB Notes for Professionals](https://goalkicker.com/MongoDBBook/) - Compiled from StackOverflow Documentation (PDF)
 * [MongoDB Succinctly, Syncfusion](https://www.syncfusion.com/resources/techportal/ebooks/mongodb) (PDF, Kindle) (email address *requested*, not required)
 * [NoSQL Databases](http://www.christof-strauch.de/nosqldbs.pdf) - Christof Strauch (PDF)
 * [The Little MongoDB Book](http://openmymind.net/2011/3/28/The-Little-MongoDB-Book/)