修复限速配置不规范，但是没有抛出异常

[zhmin]

当使用限速的时候，需要指定core.transport.channel.speed的相关配置参数，否则应该抛出异常。 并且正确的使用限速文档，已经在introduction.md修改了

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[zhmin]

如果配置不规范且没有抛出异常，会导致限速功能没用