Documentation for named tensors (#27573)
`docs/source/named_tensor.rst` is the entry point; most users will land
either here or the named tensor tutorial when looking to use named
tensors. We should strive to make this as readable, concise, and understandable
as possible.
`docs/source/name_inference.rst` lists all of the name inference rules.
It should be clear but it's hard to make it concise.
Please let me know if anything doesn't make sense and please propose
alternative wordings and/or restructuring to improve the documentation.
This should ultimately get cherry-picked into the 1.3 branch as one
monolithic commit so it would be good to get all necessary changes made
in this PR and not have any follow ups.
Test Plan:
- built and reviewed locally with `cd docs/ && make html`.
ghstack-source-id: dc2ca7a204f86d4849bd45673c189d5bbddcb32c
Pull Request resolved: https://github.com/pytorch/pytorch/pull/27173
