Rename veth plugin to ptp and add docs.

ptp (point-to-point) better describes the nature of the plugin
as veth pairs are also used by the bridge plugin.

Documentation/ptp.md

@@ -0,0 +1,28 @@
+# ptp plugin
+
+## Overview
+The ptp plugin creates a point-to-point link between a container and the host by using a veth device.
+One end of the veth pair is placed inside a container and the other end resides on the host.
+Both ends receive an IP address out of a /31 range.
+The IP of the host end becomes the gateway address inside the container.
+
+Because ptp plugin requires a pair of IP addresses for each container, it should be used in conjuction with host-local-ptp IPAM plugin.
+
+## Example network configuration
+```
+{
+	"name": "mynet",
+	"type": "ptp",
+	"ipam": {
+		"type": "host-local-ptp",
+		"subnet": "10.1.1.0/24"
+	}
+}
+
+## Network configuration reference
+
+* `name` (string, required): the name of the network
+* `type` (string, required): "ptp"
+* `ipMasq` (boolean, optional): set up IP Masquerade on the host for traffic originating from this network and destined outside of it. Defaults to false.
+* `mtu` (integer, optional): explicitly set MTU to the specified value. Defaults to value chosen by the kernel.
+* `ipam` (dictionary, required): IPAM configuration to be used for this network.