Add IRONdb remote storage adapter (#1127)

Signed-off-by: Fred Moyer <fred@redhotpenguin.com>

content/docs/operating/integrations.md

@@ -40,6 +40,7 @@ data volumes.
   * [Gnocchi](https://gnocchi.xyz/prometheus.html): write
   * [Graphite](https://github.com/prometheus/prometheus/tree/master/documentation/examples/remote_storage/remote_storage_adapter): write
   * [InfluxDB](https://docs.influxdata.com/influxdb/v1.4/supported_protocols/prometheus): read and write
+  * [IRONdb](https://github.com/circonus-labs/irondb-prometheus-adapter): read and write
   * [OpenTSDB](https://github.com/prometheus/prometheus/tree/master/documentation/examples/remote_storage/remote_storage_adapter): write
   * [PostgreSQL/TimescaleDB](https://github.com/timescale/prometheus-postgresql-adapter): read and write
   * [SignalFx](https://github.com/signalfx/metricproxy#prometheus): write