[FX] Added docstring for concrete_args (#53151)
Summary:
An oversight.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/53151
Reviewed By: jamesr66a
Differential Revision: D26766450
Pulled By: Chillee
fbshipit-source-id: 26e6e44386bbff4bc06b41c39dff9e02cadfcc73
