Updated README.md

Author: vitalii-t

README.md

@@ -325,7 +325,7 @@ public class FullFeaturedExample {
 
 Refer to the [`examples`](examples) folder for the source code of this and other advanced examples.
 
-### API Reference
+### API Reference and supported functionality
 
 You can find the API reference [here](https://mailtrap.github.io/mailtrap-java/index.html).