plugins/acl: Document how to use group statements to make rulesets

Author: cmouse

docs/core/plugins/acl.md

@@ -113,6 +113,39 @@ namespace shared {
 #acl_username = %{master_user}
 ```
 
+### Creating rulesets with group
+
+You can also simplify ACL ruleset management by defining rulesets.
+These rulesets cannot be inherited or mixed, but they should simplify the configuration,
+especially when there is large number of mailboxes to configure.
+
+```[dovecot.conf]
+# define rulesets
+
+group @acl_ruleset ruleset1 {
+   acl user=user1 {
+     rights = lri
+   }
+}
+
+group @acl_ruleset ruleset2 {
+   acl user=user1 {
+     rights = lri
+   }
+}
+
+namespace public {
+   mailbox "Secret" {
+     @acl_ruleset = ruleset1
+   }
+   mailbox "TopSecret" {
+     @acl_ruleset = ruleset2
+   }
+   mailbox "Foo*" {
+     @acl_ruleset = ruleset1
+   }
+}
+
 ## Master Users
 
 ::: info