refer to postgresql docs in debugging, which we rename "monitoring warnings"

tsa/howto/backup.mdwn

@@ -702,8 +702,12 @@ Restore LDAP databases
 
 See [[ldap]] for LDAP-specific procedures.
 
-Debug jobs
-----------
+
+Monitoring warnings
+-------------------
+
+Hint: see also the [[postgresql]] documentation for the backup
+procedures specific to that database.
 
 If a job is behaving strangely, you can inspect its job log to see
 what's going on. For example, today Nagios warned about the backups