Add brief overview to readme
# Poseidon: Machine Learning - Phase II
+## Overview
+This contains [Vent](https://github.com/CyberReboot/vent) plugins for evaluating
+machine learning models on network data as part of the
+[Poseidon](https://github.com/CyberReboot/poseidon) SDN project.
+
+## Plugins
+The current supported plugins are:
+### NodeClassifier
+Plugin for traffic classification to determine device types.
+### AbnormalDetector
+Plugin for detecting if a device is not acting normally.
+
