adding a quick link to nvfuser README.md in jit doc for 1.12 release (#78160)
adding a link to github 1.12 release branch nvfuser README.md in jit doc
Note that this PR is intended to be cherry-picked by 1.12 release, we'll have a follow up PR to update the link once this PR is merged.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/78160
Approved by: https://github.com/davidberard98
