Improves Documentation for Group Clusters

doc/api/group_clusters.md

@@ -8,6 +8,11 @@ info: To determine the technical writer assigned to the Stage/Group associated w
 
 > [Introduced](https://gitlab.com/gitlab-org/gitlab-foss/-/merge_requests/30213) in GitLab 12.1.
 
+Similar to [project-level](../user/project/clusters/index.md) and
+[instance-level](../user/instance/clusters/index.md) Kubernetes clusters,
+group-level Kubernetes clusters allow you to connect a Kubernetes cluster to
+your group, enabling you to use the same cluster across multiple projects.
+
 Users need at least [Maintainer](../user/permissions.md) access for the group to use these endpoints.
 
 ## List group clusters