Document WorkerInfo and RpcBackendOptions structures in RPC docs. (#31077)
Summary:
We mention `WorkerInfo` and `RpcBackendOptions` in a couple of different locations in our docs, and these are public classes that the user may use, so we should add the class to the documentation.
<img width="978" alt="Screen Shot 2019-12-10 at 1 42 22 PM" src="https://user-images.githubusercontent.com/8039770/70571759-47db2080-1b53-11ea-9d61-c83985a29dd9.png">
Pull Request resolved: https://github.com/pytorch/pytorch/pull/31077
Differential Revision: D18928162
Pulled By: rohan-varma
fbshipit-source-id: 67f11eedd87523c469377b791a0ba23704ec3723
