Show help for any command.

def help(ctx, topic, **kw):
    """Show help for any command.
    """
    # The help command implementation is taken from
    # https://www.burgundywall.com/post/having-click-help-subcommand
    if topic is None:
        click.echo(ctx.parent.get_help())
    else:
        click.echo(main.commands[topic].get_help(ctx))