Add presentation link to README.md

Author: iluwatar

hexagonal/README.md

@@ -29,9 +29,12 @@ Use Hexagonal Architecture pattern when
 ## Tutorials
 * [Build Maintainable Systems With Hexagonal Architecture](http://java-design-patterns.com/blog/build-maintainable-systems-with-hexagonal-architecture/)
 
+## Presentations
+* [Hexagonal Architecture](https://github.com/iluwatar/java-design-patterns/tree/master/hexagonal/etc/presentation.html)
+
 ## Real world examples
 
-* [Apache Isis](https://isis.apache.org/)
+* [Apache Isis](https://isis.apache.org/) builds generic UI and REST API directly from the underlying domain objects
 
 ## Credits