Add DEBUG variable doc

Readme more precise

monitoring/README.md

@@ -10,6 +10,10 @@ With wget :
 
 # Variables
 
-_DRYRUN='on' , example :
+_DRYRUN='on' : Display the email at the end instead of running it. Example :
 
     curl -s https://gitlab.altinea.fr/altinea/install-scripts/raw/branch/master/monitoring/altinea_monitoring_request.sh |_DRYRUN='on' sh
+
+_DEBUG='on' : print some informations about what the script is doing. Example :
+
+    curl -s https://gitlab.altinea.fr/altinea/install-scripts/raw/branch/master/monitoring/altinea_monitoring_request.sh |_DEBUG='on' sh