Add "The Boost C++ Libraries", Boris Schäling

free-programming-books.md

@@ -458,7 +458,7 @@
 * [Software Design Using C++](http://cis.stvincent.edu/html/tutorials/swd/) - Br. David Carlson and Br. Isidore Minerd
 * [Introduction to Design Patterns in C++ with Qt](http://ptgmedia.pearsoncmg.com/images/9780131879058/downloads/0131879057_Ezust_book.pdf)
 * [Data Structures and Algorithms with Object-Oriented Design Patterns in C++](http://www.brpreiss.com/books/opus4/index.html)
-
+* [The Boost C++ libraries](http://en.highscore.de/cpp/boost)
 
 ###Clojure
 * [A Brief Beginner’s Guide To Clojure](http://www.unexpected-vortices.com/clojure/brief-beginners-guide/)