Example could be more idiot-proof - go paths, protoc installation

As a total go n00b it took me an embarrassing amount of time to get the toy example app working (regenerating the protos). I suggest two improvements:

1. Better instructions for installing the golang protobuf compiler. The example app points us at https://github.com/golang/protobuf, which may as well be in Klingon to a non-gopher. For mac, all you need to do it seems is `brew install protobuf` and `protoc` is magically present (I had it already - the "golang compiler" step was a red herring). Installing golang itself is also, obviously, needed.

2. Golang appears to have its own special path for executables, and go get installs things in `~/go/bin`, and if you don't have that in your PATH then the build will fail. For me, it was as simple as adding `export PATH=/Users/james/go/bin:$PATH` to the bottom of my `.zshrc` and re-sourcing it.

For those not accustomed to golang ways, these may be rather confusing (they were for me). Thanks!

Start by locating the example app's setup instructions and checking the referenced golang/protobuf guidance. Clarify how to install protobuf and Go, and explain that Go-installed executables such as protoc-related tools may require ~/go/bin in PATH. Done means a Go newcomer can regenerate the protos and build the toy example without guesswork.

Written by the indexing model from the issue text.