Add wbt-solutions as using company (#7292)

Author: sbu-WBT

README.md

@@ -641,6 +641,7 @@ Here are some companies/projects (alphabetical order) using OpenAPI Generator in
 - [TUI InfoTec GmbH](http://www.tui-infotec.com/)
 - [unblu inc.](https://www.unblu.com/)
 - [Veamly](https://www.veamly.com/)
+- [wbt-solutions](https://www.wbt-solutions.de/)
 - [Woleet](https://www.woleet.io/)
 - [WSO2](https://wso2.com/)
 - [Vouchery.io](https://vouchery.io)