update snntorch example

[jeshraghian]

ipynb file has been added.

It follows the same syntax as the Norse tutorial, though an error is thrown at the following line:

# Save to file
nir.write("nir_model.nir", nir_model)

Note: I also had to pass in sample_data into the network to make it usable, which the Norse example does not have.

[Jegp]

There's a type in the "Import a NIR graph to snTorch". Otherwise, LGTM!

[stevenabreu7]

fixed the typo, thanks Jason! Merging this