Merge pull request #4374 from dvdksn/docs/run-staticip-subnet

docs: fix static ip example, network needs a subnet

Author: thaJeztah

docs/reference/commandline/run.md

@@ -485,10 +485,12 @@ $ docker run -itd --network=my-net busybox
 ```
 
 You can also choose the IP addresses for the container with `--ip` and `--ip6`
-flags when you start the container on a user-defined network.
+flags when you start the container on a user-defined network. To assign a
+static IP to containers, you must specify subnet block for the network.
 
 ```console
-$ docker run -itd --network=my-net --ip=10.10.9.75 busybox
+$ docker network create --subnet 192.0.2.0/24 my-net
+$ docker run -itd --network=my-net --ip=192.0.2.69 busybox
 ```
 
 If you want to add a running container to a network use the `docker network connect` subcommand.
@@ -972,4 +974,4 @@ The `docker run` command is equivalent to the following API calls:
   - If that call returns a 404 (image not found), and depending on the `--pull` option ("always", "missing", "never") the call can trigger a `docker pull <image>`.
 - `/containers/create` again after pulling the image.
 - `/containers/(id)/start` to start the container.
-- `/containers/(id)/attach` to attach to the container when starting with the `-it` flags for interactive containers.
+- `/containers/(id)/attach` to attach to the container when starting with the `-it` flags for interactive containers.