add memory usage output

tester.rb

@@ -36,3 +36,5 @@ puts '---'
 puts alias_person.find {|map| map.mail == 'georg@steffers.org'}.inspect
 puts '---'
 puts account.find {|acc| acc.mail == 'drachenfrau@steffers.org'}.inspect
+
+puts 'Memory useage: ' + `ps -o rss= -p #{Process.pid}`