[Durable Objects] Adding warning for calling setAlarm from inside the constructor (cloudflare#22746)

* Adding warning for calling setAlarm from inside
the DO constructor.

* Clarification of wording

Author: Oxyjun

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

@@ -45,6 +45,12 @@ Alarms can be used to build distributed primitives, like queues or batching of w
   - Set the time for the alarm to run. Specify the time as the number of milliseconds elapsed since the UNIX epoch.
   - If you call `setAlarm` when there is already one scheduled, it will override the existing alarm.
 
+:::caution[Calling `setAlarm` inside the constructor]
+If you wish to call `setAlarm` inside the constructor of a Durable Object, ensure that you are first checking whether an alarm has already been set.
+
+This is due to the fact that, if the Durable Object wakes up after being inactive, the constructor is invoked before the [`alarm` handler](/durable-objects/api/alarms/#alarm). Therefore, if the constructor calls `setAlarm`, it could interfere with the next alarm which has already been set.
+:::
+
 ### `deleteAlarm`
 
 - `deleteAlarm()`: <Type text='void' />