Networking API and UX documentation

More doc updates will follow

Signed-off-by: Madhu Venugopal <madhu@docker.com>

docs/extend/plugins_network.md

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+# Docker network driver plugins
+
+Docker supports network driver plugins via 
+[LibNetwork](https://github.com/docker/libnetwork). Network driver plugins are 
+implemented as "remote drivers" for LibNetwork, which shares plugin 
+infrastructure with Docker. In effect this means that network driver plugins 
+are activated in the same way as other plugins, and use the same kind of 
+protocol.
+
+## Using network driver plugins
+
+The means of installing and running a network driver plugin will depend on the
+particular plugin.
+
+Once running however, network driver plugins are used just like the built-in
+network drivers: by being mentioned as a driver in network-oriented Docker
+commands. For example,
+
+    docker network create -d weave mynet
+
+Some network driver plugins are listed in [plugins.md](/docs/extend/plugins.md)
+
+The network thus created is owned by the plugin, so subsequent commands
+referring to that network will also be run through the plugin such as,
+
+    docker run --net=mynet busybox top
+
+## Network driver plugin protocol
+
+The network driver protocol, additional to the plugin activation call, is
+documented as part of LibNetwork:
+[https://github.com/docker/libnetwork/blob/master/docs/remote.md](https://github.com/docker/libnetwork/blob/master/docs/remote.md).
+
+# Related GitHub PRs and issues
+
+Please record your feedback in the following issue, on the usual
+Google Groups, or the IRC channel #docker-network.
+
+ - [#14083](https://github.com/docker/docker/issues/14083) Feedback on
+   experimental networking features