Unmaintained readme update.

README.md

@@ -1,5 +1,10 @@
 # Prometheus OpenVPN exporter
 
+**Please note:** This repository is currently unmaintained. Due to insufficient time and not using the exporter anymore
+we decided to archive this project.
+
+---
+
 This repository provides code for a simple Prometheus metrics exporter
 for [OpenVPN](https://openvpn.net/). Right now it can parse files
 generated by OpenVPN's `--status`, having one of the following formats: