Add a license and a readme.

README.md

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+# Prometheus OpenVPN exporter
+
+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:
+
+* Client statistics,
+* Server statistics with `--status-version 2` (comma delimited),
+* Server statistics with `--status-version 3` (tab delimited).
+
+As it is not uncommon to run multiple instances of OpenVPN on a single
+system (e.g., multiple servers, multiple clients or a mixture of both),
+this exporter can be configured to scrape and export the status of
+multiple status files, using the `-openvpn.status_paths` command line
+flag. Paths need to be comma separated.
+
+Please refer to this utility's `main()` function for a full list of
+supported command line flags.