colo-compare: Update the COLO document to add the IOThread configuration

Update colo-proxy.txt,add IOThread configuration.
Later we have to configure IOThread,if not COLO can not work.

Reviewed-by: Zhang Chen <zhangchen.fnst@cn.fujitsu.com>
Signed-off-by: Wang Yong <wang.yong155@zte.com.cn>
Signed-off-by: Wang Guang <wang.guang55@zte.com.cn>
Signed-off-by: Jason Wang <jasowang@redhat.com>