Go: lib/env programs should document their config format in --help

[kormat]

For a normal unix service, you can run the binary with --help to see what options are available. With the go sciond/ps, --help only tells you about --config, but gives no clue what can/should go into the config. The only way to discover this currently is to read the source. It would be really good for --help to output a full example config with comments describing what each field/section is for.