Adding alarm handler method into DO base class.

Author: Oxyjun

src/content/docs/durable-objects/api/base.mdx

@@ -37,7 +37,13 @@ export class MyDurableObject extends DurableObject {
 
 - <code>alarm()</code>: <Type text="Promise <void>"/>
 
-  - See [Alarms](/durable-objects/api/alarms/).
+  - Called by the system when a scheduled alarm time is reached.
+
+  - The `alarm()` handler has guaranteed at-least-once execution and will be retried upon failure using exponential backoff, starting at 2 second delays for up to 6 retries. Retries will be performed if the method fails with an uncaught exception.
+
+  - This method can be `async`.
+
+  - Refer to [Alarms](/durable-objects/api/alarms/#alarm) for more information.
 
 ### `webSocketMessage`