Update config.ini template to reference etc_dir

Previously the config.ini template referenced the @config_dir and then ascended
a directory to its parent, which is @etc_dir. This commit updates the template
to use @etc_dir, as that is clearer and less confusing, while equivalent in
functionality.
Merge pull request #469 from haus/use_etc_dir_in_config_ini_template

Update config.ini template to reference etc_dir