Update Transformer.py comments to include a full example (#25411)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/25411
We provide a full example in Transformer.py in comments section.
Test Plan: N/A
Reviewed By: zhangguanheng66
Differential Revision: D17116514
fbshipit-source-id: b8fd331bef7a626e52f3347c88adba21b1f43ec5
