Sending error and usage output to stderr is common practice for command-line tools because historically many of them were designed for chaining, where the stdout of one could be sent to another, so printing help/usage to stdout could break that chaining.

That's probably why the default channel for FlagSet is stderr.

I don't think that src is designed for chaining, so changing help/usage output to stdout should be ok, but I'll check internally.

@camdencheek pointed out that even if src is used in chaining (might be for things like src search), sending help/usage to stdout doesn't break that, and errors are still sent to stderr

Thanks for the review @peterguy! Can you help merge this changeset? I don't have write access.

@tinvaan done!