Task: Check/add indication from PH async docs

[Josverl]

7.9 Undocumented asyncio features

These may be subject to change.

A Task instance has a .done() method that returns True if the task has terminated (by running to completion, by throwing an exception or by being cancelled).

If a task has completed, a .data bound variable holds any result which was returned by the task. If the task throws an exception or is cancelled .data holds the exception (or CancelledError).