Fix for retracing documentation which would break for n-ary operators (#71599)
Summary:
Fixes https://github.com/pytorch/pytorch/issues/68195
Updated fx.rst documentation and followed the instructions in [contributing.md](https://github.com/pytorch/pytorch/blob/master/CONTRIBUTING.md#writing-documentation) to generate html. Faced errors which looked very similar to https://github.com/pytorch/pytorch/issues/32703 but gathered from the thread that a non-0 exit is OK for documentation building and these are warnings not affecting the html generation (at least for root rst folder). The HTML output is plain without any styling, please confirm this is intentional.
Screenshot of generated html:
<img width="1438" alt="Screen Shot 2022-01-20 at 4 31 24 PM" src="https://user-images.githubusercontent.com/9580531/150439448-1a626d74-68ba-4f94-91f2-a6942959b049.png">
Pull Request resolved: https://github.com/pytorch/pytorch/pull/71599
Reviewed By: jamesr66a
Differential Revision: D33719546
Pulled By: zephirefaith
fbshipit-source-id: cc9b8ddb13cfdb9f14ebff54cf0d894a8b842aa1
(cherry picked from commit 170db5d7be005e90980c41449b6a9a4c23b3a91f)
