Fix several quantization documentation typos (#40567)
Summary:
This PR fixes several typos I noticed in the docs here: https://pytorch.org/docs/master/quantization.html. In one case there was a misspelled module [torch.nn.instrinsic.qat](https://pytorch.org/docs/master/quantization.html#torch-nn-instrinsic-qat) which I corrected and am including screenshots of below just in case.
<img width="1094" alt="before" src="https://user-images.githubusercontent.com/54918401/85766765-5cdd6280-b6e5-11ea-93e6-4944cf820b71.png">
<img width="1093" alt="after" src="https://user-images.githubusercontent.com/54918401/85766769-5d75f900-b6e5-11ea-8850-0d1f5ed67b16.png">
Pull Request resolved: https://github.com/pytorch/pytorch/pull/40567
Differential Revision: D22311291
Pulled By: ezyang
fbshipit-source-id: 65d1f3dd043357e38a584d9e30f31634a5b0995c
