docs: add promaton to users.md (argoproj#6860)

Signed-off-by: Niels ten Boom <[email protected]>

Author: nielstenboom

USERS.md

@@ -110,6 +110,7 @@ Currently, the following organizations are **officially** using Argo Workflows:
 1. [Polarpoint.io](https://polarpoint.io)
 1. [Pollination](https://pollination.cloud)
 1. [Preferred Networks](https://www.preferred-networks.jp/en/)
+1. [Promaton](https://www.promaton.com/)
 1. [Prudential](https://www.prudential.com.sg/)
 1. [Quantibio](http://quantibio.com/us/en/)
 1. [Raccoon Digital Marketing](https://raccoon.ag/)