Add missing doc for get_video_backend (#3643)
Add missing doc for get_video_backend (#3643)

Co-authored-by: Nicolas Hug <1a73af9e7ae00182733b2292511b814be66f065f@nicolas-hug.com>
Co-authored-by: Nicolas Hug <b961f2b01ca19b33b8cc7fe0d8d60c0676a9ec0a@fb.com>
pytorch/vision,pytorch/vision,pytorch/vision,pytorch/vision,pytorch/vision,pytorch/vision