Add info about network: host (#4959)

compose/compose-file/compose-file-v2.md

@@ -1418,6 +1418,11 @@ refer to it within the Compose file:
         external:
           name: actual-name-of-network
 
+#### host or none
+
+Not supposed for version 2 `docker-compose` files. Use
+[network_mode](#network_mode) instead.
+
 ## Variable substitution
 
 {% include content/compose-var-sub.md %}

compose/compose-file/index.md

@@ -1942,6 +1942,45 @@ discovery](https://github.com/docker/labs/blob/master/networking/A3-overlay-netw
 networking concepts lab on the [Overlay Driver Network
 Architecture](https://github.com/docker/labs/blob/master/networking/concepts/06-overlay-networks.md).
 
+#### host or none
+
+Use the host's networking stack, or no networking. Equivalent to
+`docker run --net=host` or `docker run --net=none`. Only used if you use
+`docker stack` commands. If you use the `docker-compose` command,
+use [network_mode](#network_mode) instead.
+
+The syntax for using built-in networks like `host` and `none` is a little
+different. Define an external network with the name `host` or `none` (which
+Docker has already created automatically) and an alias that Compose can use
+(`hostnet` or `nonet` in these examples), then grant the service access to that
+network, using the alias.
+
+```yaml
+services:
+  web:
+    ...
+    networks:
+      hostnet: {}
+
+networks:
+  hostnet:
+    external:
+      name: host
+```
+
+```yaml
+services:
+  web:
+    ...
+    networks:
+      nonet: {}
+
+networks:
+  nonet:
+    external:
+      name: none
+```
+
 ### driver_opts
 
 Specify a list of options as key-value pairs to pass to the driver for this