Add TiPrometheus(Prometheus adapter for TiKV) (#1235)

Signed-off-by: yuchang <yuchang@360.cn>

content/docs/operating/integrations.md

@@ -47,6 +47,7 @@ data volumes.
   * [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
+  * [TiKV](https://github.com/bragfoo/TiPrometheus): read and write
   * [VictoriaMetrics](https://github.com/VictoriaMetrics/VictoriaMetrics): write
   * [Wavefront](https://github.com/wavefrontHQ/prometheus-storage-adapter): write