[7.0] Clustered Singleton MDBs is Technical preview

Link: https://access.redhat.com/documentation/en-us/red_hat_jboss_enterprise_application_platform/7.0/html/developing_ejb_applications/message_driven_beans-1#clustered_singleton_mdbs
Revision: 73e9869383d51021a895a7540766c23debe927d3

In EAP 7.0 documentation it is mentioned Clustered Singleton MDBs feature which is Technical preview in 7.0. Although this information is written in the Release notes of 7.0, I think it should be mentioned also in the documentation in some warning box to be sure that customers are aware of that.

Note: In EAP 7.1 this feature is fully supported so this Jira is only for 7.0 documentation.