add memory usage output

@@ -116,3 +116,8 @@ mail = MailAccount.new({
   :home    => '/var/spool/vmail/domains'
   :home    => '/var/spool/vmail/domains'
 })
 })
 mail.save
 mail.save
+
+puts
+puts '====================================='
+# -o vsz/vsize
+puts 'Memory useage: ' + `ps -o rss= -p #{Process.pid}`