Added a note to scheduled task docs about the delay option.

Author: matt-aitken

docs/tasks/scheduled.mdx

@@ -3,6 +3,8 @@ title: "Scheduled tasks (cron)"
 description: "A task that is triggered on a recurring schedule using cron syntax."
 ---
 
+<Note>Scheduled tasks are only for recurring tasks. If you want to trigger a one-off task at a future time, you should [use the delay option](/triggering#delay).</Note>
+
 ## Defining a scheduled task
 
 This task will run when any of the attached schedules trigger. They have a predefined payload with some useful properties: