.DS_Store should be in the generated .gitignore

[steveklabnik]

This seems like a good idea. If you agree, I can make a PR :)

[alexcrichton]

I personally think that items like this should be in a global .gitignore rather than in a per-project .gitignore

[steveklabnik]

I agree in spirit but in reality nobody does it :/

[alexcrichton]

Closing due to #904 (comment)

I'm also worried about this leading to an endless list of common patterns that should be in a gitignore which we don't really want to be in the business of managing.