When you're working with git, there are many types of files which you will want to ignore in every single git project. System files like
.DS_Store or IDE files/folders like
.idea. Those files are more related to your system then your project and should therefore be ignored in a global .gitignore file.
Just create a basic
.gitignore file in (for example) your home directory
~/.gitignore and add those files to it.
Then just add it to your global git config with the following command:
$ git config --global core.excludesfile ~/.gitignore