--add-host example doesn't work as shown

In the documentation at https://github.com/docker/cli/blob/master/docs/reference/commandline/container_run.md#add-host, a python3 web server is run to server the hello file.

However, as shown, the command will run in the foreground and the user will be unable to run the rest of the commands in the same terminal session. If the user presses ctrl-c to terminate python to be able to run the container, the example won't work since the web server isn't running.

My own solution was to run python3 in the background by adding & to the command. However then I needed to kill the web server after running the container. Getting the pid and killing python isn't very elegant. Hopefully you can come up with a better solution.

Read the --add-host section in docs/reference/commandline/container_run.md and run the documented python3 web-server command alongside the container commands. Update the example so the server remains available while the commands run in the same terminal session and the instructions explain how the example is finished cleanly.