HBASE-28816 The description of "hbase.superuser" is confusing (#6206)

Signed-off-by: Duo Zhang <[email protected]>
(cherry picked from commit 46da224)

Author: eubnara

hbase-common/src/main/resources/hbase-default.xml

@@ -1185,7 +1185,8 @@ possible configurations would overwhelm and obscure the important.
     <value></value>
     <description>List of users or groups (comma-separated), who are allowed
     full privileges, regardless of stored ACLs, across the cluster.
-    Only used when HBase security is enabled.</description>
+    Only used when HBase security is enabled.
+    Group names should be prefixed with "@".</description>
   </property>
   <property>
     <name>hbase.auth.key.update.interval</name>