Currently, Poetry doesn’t have a -f option (there’s an open issue and an open PR), so you can’t use the pip instructions. You can install the .whl files directly:
poetry add https://download.pytorch.org/whl/torch_stable.html/cpu/torch-1.3.1%2Bcpu-cp36-cp36m-win_amd64.whl
or add the dependency directly to your .toml file:
[tool.poetry.dependencies]
torch = { url = "https://download.pytorch.org/whl/torch_stable.html/cpu/torch-1.3.1%2Bcpu-cp36-cp36m-win_amd64.whl" }