Adds mention of Userlist to the README.md

README.md

@@ -268,3 +268,11 @@ The gem is available as open source under the terms of the [MIT License](https:/
 ## Code of Conduct
 
 Everyone interacting in the ActiveModel::Relation project's codebases, issue trackers, chat rooms and mailing lists is expected to follow the [code of conduct](https://github.com/userlist/active_model-relation/blob/main/CODE_OF_CONDUCT.md).
+
+## What is Userlist?
+
+[![Userlist](https://userlist.com/images/external/userlist-logo-github.svg)](https://userlist.com/)
+
+[Userlist](https://userlist.com/) allows you to onboard and engage your SaaS users with targeted behavior-based campaigns using email or in-app messages.
+
+Userlist was started in 2017 as an alternative to bulky enterprise messaging tools. We believe that running SaaS products should be more enjoyable. Learn more [about us](https://userlist.com/about-us/).