minor doc, better format in howto_docs.md
minor doc, better format in howto_docs.md

haoch/kylin,haoch/kylin,haoch/kylin,murkrishn/incubator-kylin,murkrishn/incubator-kylin,murkrishn/incubator-kylin,lemire/incubator-kylin,lemire/incubator-kylin,lemire/incubator-kylin,lemire/incubator-kylin,haoch/kylin,murkrishn/incubator-kylin,haoch/kylin,haoch/kylin