The .gitignore file is missing _config_user

[zachparrott]

In the .gitignore file currently it has the following:

# exclude config
pyEPR/config.py

..but config.py is not the name of the config file. It should correctly match _config_user.py so people can have a modified local configuration of material parameters and root directory and what not and still be able to contribute to the main package without having unnecessary other files being tracked.