added link

Author: thombergs

rxjava-2/README.md

@@ -6,3 +6,4 @@
 - [RxJava Maybe](http://www.baeldung.com/rxjava-maybe)
 - [Introduction to RxRelay for RxJava](http://www.baeldung.com/rx-relay)
 - [Combining RxJava Completables](https://www.baeldung.com/rxjava-completable)
+- [Converting Synchronous and Asynchronous APIs to Observables using RxJava2](https://www.baeldung.com/rxjava-apis-to-observables)