Add Fenergo in companies using OpenApi Generator (#4192)

Author: albertocorrales

README.md

@@ -557,6 +557,7 @@ Here are some companies/projects (alphabetical order) using OpenAPI Generator in
 - [Cupix](https://www.cupix.com/)
 - [DB Systel](https://www.dbsystel.de)
 - [Element AI](https://www.elementai.com/)
+- [Fenergo](https://www.fenergo.com/)
 - [FormAPI](https://formapi.io/)
 - [Fuse](https://www.fuse.no/)
 - [Gantner](https://www.gantner.com)