https://pytorch.org/torchtune/stable/basics/instruct_datasets.html
I based my work (first ever torchtune attempt) on the first example on this page, and had an error until I added _component_: torchtune.datasets.instruct_dataset
which is in the later examples but not the first one.
Also, as a general note, it took a surprising amount of looking starting from the "first fine-tune" tutorial (https://pytorch.org/torchtune/stable/tutorials/first_finetune_tutorial.html#) and the how-too guide (https://www.llama.com/docs/how-to-guides/fine-tuning/) to start answering the (IMO important!) question of: "How do I specify what data to train on?!?"