Document updates and outbox features in workflows

Added documentation for updates and outbox features in workflows, including examples of defining update methods and using the outbox to manage outgoing messages.

Author: rmcdaniel

docs/features/queries.md

@@ -39,3 +39,59 @@ $ready = $workflow->getReady();
 <QuerySimulator />
 
 **Important:** Querying a workflow does not advance its execution, unlike signals.
+
+# Updates
+
+Updates allow you to retrieve information about the current state of a workflow and mutate the workflow state at the same time. They are essentially both a query and a signal combined into one.
+
+To define an update method on a workflow, use the `UpdateMethod` annotation:
+
+```php
+use Workflow\UpdateMethod;
+use Workflow\Workflow;
+
+class MyWorkflow extends Workflow
+{
+    private bool $ready = false;
+
+    #[UpdateMethod]
+    public function updateReady($ready): bool
+    {
+        $this->ready = $ready;
+
+        return $this->ready;
+    }
+}
+```
+
+## Outbox
+
+The outbox collects outgoing query messages and lets you produce them exactly once, even if the workflow is replayed or resumed multiple times.
+
+```php
+use Workflow\UpdateMethod;
+use Workflow\Workflow;
+
+class MyWorkflow extends Workflow
+{
+    #[UpdateMethod]
+    public function receive()
+    {
+        if ($this->outbox->hasUnsent()) {
+            return $this->outbox->nextUnsent();
+        }
+    }
+
+    public function execute()
+    {
+        $count = 0;
+        while (true) {
+            $count++;
+
+            $this->outbox->send("Message {$count");
+        }
+    }
+}
+```
+
+Each sent signal is stored in the outbox. The outbox tracks which messages have already been sent. On replay, previously read messages remain sent. Only unsent messages are returned by `nextUnsent()`. This makes the outbox safe to send multiple messages inside long-running loops.