Add deprecation warning to the readme file.

README.md

-edX Insights
-===========
+edX Insights Early Prototype
+============================
+
+***Warning***: This repository contains an early prototype of the edX analytics
+infrastructure. The code base for the current version of the
+[Insights](http://edx-insights.readthedocs.org/en/latest/) product can
+be found in the following repositories:
+
+* https://github.com/edx/edx-analytics-dashboard
+* https://github.com/edx/edx-analytics-data-api
+* https://github.com/edx/edx-analytics-pipeline
+
+---
 
 This is a development version of an analytics framework for the edX
 infrastructure. It will replace the ad-hoc analytics used in the