Updates set_default_dtype documentation (#63233)
Summary:
Fixes https://github.com/pytorch/pytorch/issues/60560.
The description of set_default_dtype is updated to clarify that it affects the interpretation of Python numbers as either float32 (complex64) or float64 (complex128) and that default (floating) dtypes other than float32 or float64 are unsupported.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/63233
Reviewed By: VitalyFedyunin
Differential Revision: D30306396
Pulled By: mruberry
fbshipit-source-id: bbee62f323c773b23b2fa45cb99122bc28197432
