Add .curlrc

[`.curlrc`](http://curl.haxx.se/docs/manpage.html#FILES): [cURL](http://en.wikipedia.org/wiki/CURL) default configuration file.

@mattbanks: according to the [docs](http://curl.haxx.se/docs/manpage.html#-K) (haven't tested it), on Windows, `_curlrc` is used instead of `.curlrc` so, you might consider adding it.