Add some comments to help use munin plugin, add over limit detection

munin/nominatim_importlag

@@ -5,12 +5,26 @@
 # Can be configured through libpq environment variables, for example
 # PGUSER, PGDATABASE, etc. See man page of psql for more information
 #
+# To configure munin for a default installation, add these lines to
+# the file /etc/munin/plugin-conf.d/munin-node or in any file in the
+# directory /etc/munin/plugin-conf.d/
+#
+# [nominatim_*]
+# user www-data
+# env.PGUSER www-data
+# env.PGPORT 5432
+# env.PGDATABASE nominatim
+# env.age_warning 21600
+# env.age_critical 86400
+
 # Parameters:
 #
 #       config   (required)
 #       autoconf (optional - used by munin-config)
 #
 
+. $MUNIN_LIBDIR/plugins/plugin.sh
+
 if [ "$1" = "config" ]; then
 
         echo 'graph_title Data import lag'
@@ -20,6 +34,8 @@ if [ "$1" = "config" ]; then
         echo 'age.label DB import age'
         echo 'age.type GAUGE'
         echo 'age.cdef age,60,/'
+        print_warning age
+        print_critical age
         exit 0
 fi