docs: auto generate Dragonfly cli/api docs via code

Signed-off-by: pouchrobot <pouch-dev@list.alibaba-inc.com>

CONTRIBUTORS

@@ -28,6 +28,7 @@ Guangming Wang <guangming.wang@daocloud.io>
 Guangwen Feng <fenggw-fnst@cn.fujitsu.com>
 Haines Chan <zhinhai@gmail.com>
 Haosdent Huang <haosdent@gmail.com>
+Hu Shuai <hus.fnst@cn.fujitsu.com>
 huaxiao <huaxiao@jd.com>
 Hui Zhao <176425810@qq.com>
 hwdef <hwdef97@gmail.com>
@@ -79,4 +80,5 @@ zuozheng.hzz <zuozheng.hzz@alibaba-inc.com>
 也行 <yexing.gw@alibaba-inc.com>
 宋文杰 <wenjie.song@daocloud.io>
 岁月摧锋断吴钩 <GammaRay@foxmail.com>
+慕陶 <jihui.xjh@antfin.com>
 陈潮兵 <chenchaobing@126.com>

docs/cli_reference/dfget.md

@@ -43,7 +43,7 @@ download SUCCESS cost:0.026s length:141898 reason:0
   -f, --filter string         filter some query params of URL, use char '&' to separate different params
                               eg: -f 'key&sign' will filter 'key' and 'sign' query param
                               in this way, different but actually the same URLs can reuse the same downloading task
-      --header strings        http header, eg: --header='Accept: *' --header='Host: abc'
+      --header stringArray    http header, eg: --header='Accept: *' --header='Host: abc'
   -h, --help                  help for dfget
       --home string           the work home directory of dfget
   -i, --identifier string     the usage of identifier is making different downloading tasks generate different downloading task IDs even if they have the same URLs. conflict with --md5.