You should be able to! But we just saw that it isn't supported as part of the dataset interface, only on the task interface. So you can get the datasets's underlying task for now and add a comment this way:
your_dataset._task.comment = "your text here"
We have flagged this as a bug and we'll add this soon!
Thank you, I'll report if its work on Sunday
JitteryParrot8 in the new SDK we'll have dataset.add_description() which will do the same as KindChimpanzee37 provided but with a nicer interface 😄