doc: add agent case in welcome page (#471)

* doc: add agent case in welcome page

* fix

Author: jiashengguo

docs/welcome.md

@@ -15,6 +15,7 @@ Some of the most common use cases of ZenStack include:
 - Multi-tenant SaaS
 - Applications with complex access control requirements
 - CRUD-intensive API or web apps
+- AI agents handle CRUD database operations
 
 ZenStack is not opinionated about your choice of framework. It can be used with any of them.