Update README.md

Author: miccol

README.md

@@ -3,6 +3,28 @@ BT++ ![License MIT](https://img.shields.io/dub/l/vibe-d.svg)
 ![Version](https://img.shields.io/badge/version-v1.4-green.svg) <br/> 
 A behavior tree library in `C++`.
 
+REFERENCE
+------------
+Please refer to the following paper when using the library:
+
+**How Behavior Trees Modularize Hybrid Control Systems and Generalize Sequential Behavior Compositions, the Subsumption Architecture, and Decision Trees.** Michele Colledanchise and Petter Ogren. IEEE Transaction on Robotics 2016.
+
+bibtex entry:
+
+`@ARTICLE{7790863, 
+author={M. Colledanchise and P. Ögren}, 
+journal={IEEE Transactions on Robotics}, 
+title={How Behavior Trees Modularize Hybrid Control Systems and Generalize Sequential Behavior Compositions, the Subsumption Architecture, and Decision Trees}, 
+year={2017}, 
+volume={33}, 
+number={2}, 
+pages={372-389}, 
+keywords={Computer architecture;Decision trees;High definition video;Robot control;Switches;Behavior trees (BTs);decision trees;finite state machines (FSMs);hybrid dynamical systems (HDSs);modularity;sequential behavior compositions;subsumption architecture}, 
+doi={10.1109/TRO.2016.2633567}, 
+ISSN={1552-3098}, 
+month={April},}`
+
+
 BUILD STATUS
 ------------