Fix RRef design doc warning (#30240)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/30240
Get rid of the following warning when build docs:
```
/Users/shenli/Project/pytorch/docs/source/notes/rref.rst:184: WARNING: Error in "code" directive:
maximum 1 argument(s) allowed, 6 supplied.
.. code::
import torch
import torch.distributed.rpc as rpc
# on worker A
rref = rpc.remote('B', torch.add, args=(torch.ones(2), 1))
# say the rref has RRefId 100 and ForkId 1
rref.to_here()
```
Test Plan: Imported from OSS
Differential Revision: D18640016
Pulled By: mrshenli
fbshipit-source-id: d527827f01183411d4b4c73e0a976bdd7fccbf49
