Also please only modify one file per commit. This'll make merging easier for everyone.
Global gitignores (OS-specific, editor-specific) should go into the
For more information on gitignore: gitignore(5)
git has a global configuration that applies rules to all of your projects. For example:
git config --global core.excludesfile ~/.global_ignore
... will apply the rules in ~/.global_ignore for all of your repos.
This is useful if you use an editor (like Emacs) that drops backup files, or if you work in an environment that generates binary or intermediate files that are always ignored.