updata how set docker on ubuntu16.04
the old method "Alternatively" is invaild on ubuntu16.04,but the
new method is vaild.
#done
@@ -25,6 +25,14 @@ Edit systemd service config file `/lib/systemd/system/docker.service`, update th
ExecStart=/usr/bin/dockerd -H fd:// -H unix:///var/run/docker.sock -H tcp://0.0.0.0:2375 --default-ulimit=nofile=8192:16384 --default-ulimit=nproc=8192:16384
```
+#### Ubuntu 16.04
+Edit systemd service config file `usr/lib/systemd/system/docker.service`, update the `ExecStart` line under section `[Service]`, as the following:
+
+```
+[Service]
+ExecStart=/usr/bin/dockerd -H fd:// -H unix:///var/run/docker.sock -H tcp://0.0.0.0:2375 --default-ulimit=nofile=8192:16384 --default-ulimit=nproc=8192:16384
+```
+
Regenerate the docker service script and restart the docker engine:
```bash
