Rewrite container run help

Several bad cases here:

```
  ports: An object mapping ports to an empty object in the
        form:

        {"<port>/<tcp|udp|sctp>": {}}
```

```
  env: A list of environment variables to set inside the
        container in the form ["VAR=value", ...]. A variable without
        = is removed from the environment, rather than to have an
        empty value.
```