Re-introduce the functorch docs build (#85838) (#86125)
We deleted it when merging functorch into pytorch. This PR makes a new
functorch docs build.
The docs are relatively simple:
- cd into `functorch/docs` and run `make html` to build the docs.
- docs should get pushed to the pytorch/functorch repo's gh-pages
branch.
The long term plan is:
- one day, the functorch APIs will just be torch.* APIs, at which point
we can fold all of the functorch docs into the regular PyTorch docs
- When that happens, the functorch examples and tutorials (that are on
the functorch docs site) can be moved to the pytorch examples and
pytorch tutorials.
Test Plan:
- check docs preview
- watch this PR after it goes in
Differential Revision: [D40026222](https://our.internmc.facebook.com/intern/diff/D40026222)
Pull Request resolved: https://github.com/pytorch/pytorch/pull/86125
Approved by: https://github.com/atalman, https://github.com/malfet
