add a icinga2 summary section

admin-guide/configuration/icinga2.md

@@ -7,6 +7,38 @@ The overview of your nodes in Icinga2 you get at [monitoring.psi.ch](https://mon
 But the configuration as such is not done therein, but in Hiera and automatically propagated.
 
 
+## TL;DR
+
+I, admin of xyz.psi.ch want ...
+
+... **monitoring with e-Mails during office hours**:
+```
+icinga2::enable: true
+icinga2::agent::enable: true
+icinga2::alerting::enable: true
+```
+
+... **monitoring with SMS all around the clock**:
+```
+icinga2::enable: true
+icinga2::agent::enable: true
+icinga2::alerting::enable: true
+icinga2::alerting::severity: 1
+```
+
+... **just be able to check monitoring state on monitoring.psi.ch**:
+```
+icinga2::enable: true
+icinga2::agent::enable: true
+icinga2::alerting::enable: false
+icinga2::alerting::severity: 5
+```
+
+... **no monitoring**:
+```
+icinga2::enable: false
+```
+
 ## Basic Configuration
 Enable monitoring with Icinga2 by
 ```