Add NOPROXY note

Proxy setting feature is added by #6 

If we want to use proxy, we must set "NOPROXY". But this specification is not written anywhere. This is confusing!

So I wrote this note.

![2014-09-18 0 59 01](https://cloud.githubusercontent.com/assets/608755/4306894/74988ccc-3e84-11e4-8657-be883896a9b5.png)