git usefull links for ignoring files

https://help.github.com/articles/ignoring-files

A global .gitignore file can also be used by adding one to your global git config. For example, you might create the file
~/.gitignore_global
and add some rules to it. To add this to your config, run
git config --global core.excludesfile ~/.gitignore_global

grab the Objective-C.gitignore

from this git repository
https://github.com/github/gitignore