Need go examples on auth.md

[James Miller]

I'm having much more trouble than I should be having figuring out how to get simple server-side TLS going with go (golang). Can someone add a a few snippets? Thanks.

[Eric Anderson]

It seems Go is missing from https://grpc.io/docs/guides/auth.html

[Jan Tattermusch]

@dfawley can we fix as part of the fixit?