Document the --no-multicast-route flag

site/features.md

@@ -50,6 +50,8 @@ TCP/IP, e.g. a netcat UDP service would be run with
 
     root@a2:/# echo 'Hello, world.' | nc -u a1 5533
 
+Broadcast and multicast protocols also work over Weave Net.
+
 We can deploy the entire arsenal of standard network tools and
 applications, developed over decades, to configure, secure, monitor,
 and troubleshoot our container network. To put it another way, we can

site/plugin.md

@@ -84,6 +84,10 @@ The plugin command-line arguments are:
  * `--no-multicast-route`: stop weave adding a static IP route for
    multicast traffic on its interface
 
+By default, multicast traffic will be routed over the weave network.
+To turn this off, e.g. because you want to configure your own multicast
+route, add the `--no-multicast-route` flag to `weave launch-plugin`.
+
 ## Restarting
 
 We start the plugin with a restart policy, because Docker attempts to

site/proxy.md

@@ -115,6 +115,10 @@ will only include one of them.
 
     host1$ weave launch-router && weave launch-proxy --rewrite-inspect
 
+By default, multicast traffic will be routed over the weave network.
+To turn this off, e.g. because you want to configure your own multicast
+route, add the `--no-multicast-route` flag to `weave launch-proxy`.
+
 ## <a name="ipam"></a>Automatic IP address assignment
 
 If [automatic IP address assignment](ipam.html) is enabled in weave,