document byte stream logging

[rrayst]

by adding

        <RollingFile name="TRAFFIC" fileName="/tmp/traffic.log" filePattern="/tmp/traffic-%i.log" >
            <PatternLayout pattern="%d{ABSOLUTE} %5p %tid %tn %c{1}:%L - %m%n" />
            <Policies>
                <SizeBasedTriggeringPolicy size="100M" />
            </Policies>
            <DefaultRolloverStrategy max="10" />
        </RollingFile>

and

        <Logger name="com.predic8.membrane.core.transport.http.ByteStreamLogging" level="trace" additivity="false">
            <AppenderRef ref="TRAFFIC" />
        </Logger>

to your log4j2.xml, you can enable byte stream logging.