README: add screenshots

fixes #87

README.md

@@ -5,10 +5,16 @@ If you want to visualize and monitor hierarchical business processes based on
 any or all objects monitored by Icinga, the Icinga Web 2 business process
 module is the way to go.
 
+![Tree View](doc/screenshot/00_preview/0001_preview-tree-view.png)
+![Tile View](doc/screenshot/00_preview/bb_preview_tile_view.png)
+
 Want to create custom process-based dashboards? Trigger notifications at
 process or sub-process level? Provide a quick top-level view for thousands of
 components on a single screen? That's what this module has been designed for!
 
+![Dashboard](doc/screenshot/00_preview/aa_preview_businessprocesses_on_dashboard.png)
+![Split View](doc/screenshot/00_preview/aa_preview_tile_and_subtree.png)
+
 You're running a huge cloud, want to get rid of the monitoring noise triggered
 by your auto-scaling platform but still want to have detailed information just
 a couple of clicks away in case you need them? You will love this little module!