Update pytorch (and functorch) to 1.13.1

[machenmusik]

Note that for existing installations, the following is recommended due to complications with older versions of functorch:

• pip uninstall torch torchvision functorch
• install the correct pytorch 1.13.1 version for your CUDA installation from https://pytorch.org/get-started/locally/ but add functorch to the command -- for example, CUDA 11.7 would be pip3 install torch torchvision functorch --extra-index-url https://download.pytorch.org/whl/cu117
• reinstall tinycudann torch bindings e.g. pip install git+https://github.com/NVlabs/tiny-cuda-nn/#subdirectory=bindings/torch
• reinstall nerfstudio e.g. pip install -e . from the source directory

[machenmusik]

(Need corresponding updates to docs.)

[machenmusik]

(Not sure what the readthedocs failure is from, the details link goes to 404)

[tancik]

(Not sure what the readthedocs failure is from, the details link goes to 404)

The error is /home/docs/checkouts/readthedocs.org/user_builds/plenoptix-nerfstudio/checkouts/1390/docs/quickstart/installation.md:162: WARNING: 'myst' reference target not found: #pytorch

[machenmusik]

Thx - weird, because it is a local anchor reference that works fine e.g. https://github.com/nerfstudio-project/nerfstudio/blob/d0fe3677a460a1e467f2765c7842b16a0b2ea15f/docs/quickstart/installation.md#pytorch

Compare that to the Installation FAQ links at the bottom which are supposed to be self-referential, and don't generate errors, but are broken!

Suggestions welcome (since can't merge as-is).

[tancik]

You can run python scripts/docs/build_docs.py --clean-cache to see the error locally. If you add (pytorch)= at line 20 and remove the #, it should work.

[machenmusik]

Ok, although that breaks usage of the MD files as-is on github.