update readme

Author: ssssank

README.md

@@ -36,3 +36,8 @@ String[] secondNames = {"Igor", "Petya", "Sergey", "Vasya", "Sasha"};
 difference(firstNames, secondNames);
 // ["Kolya"]
 ```
+[![Hexlet Ltd. logo](https://raw.githubusercontent.com/Hexlet/assets/master/images/hexlet_logo128.png)](https://hexlet.io?utm_source=github&utm_medium=link&utm_campaign=java-arrays-as-sets)
+
+This repository is created and maintained by the team and the community of Hexlet, an educational project. [Read more about Hexlet](https://hexlet.io?utm_source=github&utm_medium=link&utm_campaign=java-arrays-as-sets).
+
+See most active contributors on [hexlet-friends](https://friends.hexlet.io/).