Add Heureka Group to adopters

ADOPTERS.md

@@ -9,6 +9,7 @@
 - [Container Solutions](http://container-solutions.com/)
 - [Form3](https://www.form3.tech/)
 - [Pier Insurance](https://www.pier.digital/)
+- [Heureka Group](https://heureka.group)
 
 
 Countless others that can't disclose that information! :)