Adds an OpInfo note (#57428)
Summary:
Like the title says. The OpInfo pattern can be confusing when first encountered, so this note links the Developer Wiki and tracking issue, plus elaborates on the goals and structure of the OpInfo pattern.
cc imaginary-person, who I can't add as a reviewer, unfortunately
Pull Request resolved: https://github.com/pytorch/pytorch/pull/57428
Reviewed By: SplitInfinity
Differential Revision: D29221874
Pulled By: mruberry
fbshipit-source-id: aa73228748c9c96eadf2b2397a8b2ec31383971e
