add in docs, unique queue what is it

docs/command/queue/pull_push/memory_unique.md

@@ -4,6 +4,22 @@ Memory unique queue
 It works just like the [Memory queue](memory.md), but it only allows storing unique commands. All duplicates will
 be ignored.
 
+### What is it for
+
+A queue of unique commands is needed when you need to perform an action once after a domain event. But since there can
+be many domain events, and the action must be performed only once, you need to remove all duplicate actions from the
+queue.
+
+Examples:
+
+* **Action:** Update a block of popular articles
+* **Event:** View article
+
+Views come regularly, and the block needs to be updated no more often than 10 minutes. If there are no views, then
+there is no need to update the block.
+
+### Usage
+
 ```php
 use GpsLab\Component\Command\Bus\HandlerLocatedCommandBus;
 use GpsLab\Component\Command\Handler\Locator\DirectBindingCommandHandlerLocator;

docs/command/queue/pull_push/predis_unique.md

@@ -4,6 +4,22 @@ Predis unique queue
 It works just like the [Predis queue](predis.md), but it only allows storing unique commands. All duplicates will
 be ignored.
 
+### What is it for
+
+A queue of unique commands is needed when you need to perform an action once after a domain event. But since there can
+be many domain events, and the action must be performed only once, you need to remove all duplicate actions from the
+queue.
+
+Examples:
+
+* **Action:** Update a block of popular articles
+* **Event:** View article
+
+Views come regularly, and the block needs to be updated no more often than 10 minutes. If there are no views, then
+there is no need to update the block.
+
+### Usage
+
 Configure queue:
 
 ```php