Fix cppdoc example syntax (#62385)
Summary:
a simple fix
Pull Request resolved: https://github.com/pytorch/pytorch/pull/62385
Reviewed By: suo
Differential Revision: D30000982
Pulled By: heitorschueroff
fbshipit-source-id: e2e1c9efba3734b58d9b5f358c01d12c2c8c91ff
