Including generator param in randperm documentation (#47231)
Summary:
The `randperm` documentation is outdated and did not use to include the optional `generator` parameter. This PR just adds that along with the `pin_memory` parameter.
This PR was brought up in [PR 47022](https://github.com/pytorch/pytorch/pull/47022), but is now rebased onto master.
New docs look like:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/47231
Reviewed By: mruberry
Differential Revision: D24711960
Pulled By: janeyx99
fbshipit-source-id: 3ff8be62ec33e34ef87d017ea97bb950621a3064
