Grammatically updated the tech docs (#47345)
Summary:
<img width="1440" alt="Screenshot 2020-11-04 at 1 07 21 PM" src="https://user-images.githubusercontent.com/72745540/98082455-c5f89200-1e9e-11eb-97e3-ae0eb62355f6.png">
small grammatical update to the torch tech docs.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/47345
Reviewed By: malfet
Differential Revision: D24859919
Pulled By: ejguan
fbshipit-source-id: 5c6a8bc8e785c5295bf6f2f5b583dd6054b96fec
