docs: Documentation does not render appropriately

[JosiahParry]

The equations for the loss function do not render appropriately:

torch/R/nn-loss.R

Line 28 in 7ff1cdd

#' \deqn{

Additionally, it is not clear how to use this function. It would be great if there was a minimal example in the docs as well.

[JosiahParry]

The same is here: https://torch.mlverse.org/docs/reference/nn_nll_loss

[sebffischer]

I submitted a fix for the rendering here: #1308