message: Update README.md with grafana screenshot
diff: @@ -33,6 +33,8 @@ PCM provides a number of command-line utilities for real-time monitoring:
  - **pcm-bw-histogram**: collect memory bandwidth utilization histogram
  Graphical front ends:
  +- **pcm Grafana dashboard** : front-end for Grafana (in `grafana` directory)
  +![pcm grafana output](https://raw.githubusercontent.com/wiki/opcm/pcm/pcm-dashboard.png)
  - **pcm-sensor** : front-end for KDE KSysGuard
  - **pcm-service** : front-end for Windows perfmon
  