Add CNI plugin to description

plugin/README.md

@@ -1,9 +1,14 @@
-# Weave network driver extension for Docker
+# Weave network driver extension for Docker and Kubernetes
 
-A [plugin](http://docs.docker.com/engine/extend/plugin_api/) to
-integrate [weave Net](http://weave.works/net/) with Docker.
+This directory implements both a 
+[Docker plugin](http://docs.docker.com/engine/extend/plugin_api/) to
+integrate [Weave Net](http://weave.works/net/) with Docker, and a 
+[Container Network Interface (CNI) plugin](https://github.com/appc/cni#cni---the-container-network-interface),
+to integrate Weave Net with [Kubernetes](http://kubernetes.io/).
 
-The plugin runs automatically when you `weave launch`, provided your
+The Docker plugin runs automatically when you `weave launch`, provided your
 Docker daemon is version 1.9 or newer.
 
-More detail [here](http://docs.weave.works/weave/latest_release/plugin.html).
+More detail on the Docker plugin [here](http://docs.weave.works/weave/latest_release/plugin.html).
+
+More detail on the CNI plugin [here](https://github.com/weaveworks/weave/blob/master/site/plugin/cni-plugin-how-to.md).