Add a tutorial for using gRPC on FWF

[macolso]

To raise visibility, I think we should add a tutorial about how to use gRPC (based off @fibonacci1729's work here) to the FWF TOC.

We can use services like https://grpcb.in/ to demonstrate grpc client calls

[macolso]

@ThorstenHans and I can toss a coin on who takes this one 😁