argocd: add more cases for appset (#10565)

Author: zvlb

topics/argo/README.md

@@ -308,7 +308,9 @@ So instead of creating multiple separate applications, you have the root applica
 
 * Cluster Preparation: You would like to deploy multiple applications at once to bootstrap a Kubernetes cluster
 
-TODO: add more :)
+* Multiple environments: If deploying many versions of the same application, but with minor changes. For example, several test deployments to test different features
+
+* Multiple clusters: when the same application needs to be deployed across multiple K8s clusters connected to ArgoCD
 </b></details>
 
 <details>
@@ -507,4 +509,4 @@ It's an Analysis resource that fetches response status from Prometheus (monitori
 `kubectl argo rollouts get rollout SOME-APP --watch`
 </b></details>
 
-<!-- {% endraw %} -->
+<!-- {% endraw %} -->