Add PLAID, Inc. to the user list (#7552)

Author: algas

README.md

@@ -623,6 +623,7 @@ Here are some companies/projects (alphabetical order) using OpenAPI Generator in
 - [openVALIDATION](https://openvalidation.io/)
 - [Oracle](https://www.oracle.com/)
 - [Paxos](https://www.paxos.com)
+- [PLAID, Inc.](https://plaid.co.jp/)
 - [Ponicode](https://ponicode.dev/)
 - [Pricefx](https://www.pricefx.com/)
 - [Prometheus/Alertmanager](https://github.com/prometheus/alertmanager)