Explain multiple networks

site/plugin.md

@@ -48,6 +48,11 @@ store](#cluster-store) (like Docker's overlay driver) and one named
 * Supports only a single network (we create one named `weave` for you automatically)
 * Uses Weave's partition tolerant IPAM
 
+If you do create additional networks using the `weavemesh` driver,
+containers attached to them will be able to communicate with
+containers attached to `weave`; there is no isolation between those
+networks.
+
 ### `weave` driver
 
 * This runs in what Docker call "global scope"; requires a cluster store
@@ -58,7 +63,7 @@ There's no specific documentation from Docker on using a cluster
 store, but the first part of [Getting Started with Docker Multi-host Networking][docker-net]
 should point the way.
 
-Note that in the case of multiple docker networks, all containers are
+Note that in the case of multiple networks using the `weave` driver, all containers are
 on the same virtual network but Docker allocates their addresses on
 different subnets so they cannot talk to each other directly.