Add bip confi item for ros docker/system-docker

content/os/v1.x/en/installation/configuration/docker/_index.md

@@ -36,6 +36,7 @@ Many of the standard Docker daemon arguments can be placed under the `rancher.do
 Key | Value
 ---|---
 `bridge` | String
+`bip` | String
 `config_file` | String
 `containerd` | String
 `debug` | Boolean
@@ -78,6 +79,16 @@ rancher:
     extra_args: [--mtu, 1460]
 ```
 
+#### Example using bip for docker0 bridge
+
+_Available as of v1.4.x_
+
+The docker0 bridge can be configured with docker args, it will take effect after reboot.
+
+```
+$ ros config set rancher.docker.bip 192.168.100.1/16
+```
+
 ### Configuring System Docker
 
 In your cloud-config, System Docker configuration is located under the `rancher.system_docker` key.