Doc/add readme ja translation

translate README.md for ja_JP.

btw, how can I explain * Great 'out of the box' feature set. in Features of README? 
I tried to translate it, and I think that out of the box may means "(idiomatic, of a product) Immediate(ly), without intervention from the customer. This software has to work out of the box, without any fancy installation. "
and translate like so.

if I mistake the meaning of this word, please let me know :)