Add reference for linalg.vecdot (#108188)
Was addressing https://github.com/pytorch/pytorch/issues/108127, but
then I realised that vecdot is already CompositeImplicit. Pushing anyway
as a short-and-sweet PR.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/108188
Approved by: https://github.com/peterbell10
