message: add link to grafana directory in the main README
diff: @@ -34,7 +34,7 @@ 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 dashboard** : front-end for Grafana (in [grafana](https://github.com/opcm/pcm/tree/master/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
  