International friendly README

As mentioned in #14 .

I also updated the `lang` attribute in html template because it will cause annoying translating message on Chrome:
![image](https://cloud.githubusercontent.com/assets/2840571/3732039/f9b90dde-16f5-11e4-9b2c-56d4c0f20572.png)

I'm not really sure in what situation we will need to set `lang="ja"`?
If we set `lang="en-US"`, it might not cause any weird thing, right?