add doc for customizing logging config
add doc for customizing logging config

channelcat/sanic,yunstanford/sanic,lixxu/sanic,lixxu/sanic,lixxu/sanic,yunstanford/sanic,channelcat/sanic,yunstanford/sanic,channelcat/sanic,lixxu/sanic,yunstanford/sanic,ashleysommer/sanic,ashleysommer/sanic,channelcat/sanic,ashleysommer/sanic