Add alerts section of user manual

doc/source/armadito-glpi/manual/alerts/index.rst

@@ -4,5 +4,22 @@ Alerts
 Board
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+It is here possible to know which antivirus detects more viruses in your IT infrastructure.
+While it is not the initial purpose, it could be used as a realtime antiviruses comparison tool.
+You can also detects what kind of virus has spread the most.
+
+For now, there is three charts :
+
+* **AlertsByVirusNameChart** : shows alerts repartition by threat name
+* **LastAlertsChart** : shows alerts traffic of last hours
+* **AlertsByAntivirusChart** : shows alerts repartition by antivirus name
+
 Alerts
 ------
+
+That section is where centralized alerts can be monitored.
+For example, you can search for some specific alerts coming from multiple antiviruses, from multiple operating systems.
+Furthermore, you can manipulate these alerts by removing/restoring them as you wish.
+
+More features will be easy to add because of the way "massive actions" are implemented in GLPI.
+We could later imagine features like sending a group of alerts by email, etc.