Convert jp rdoc to md

Hi,

I've converted this, but large sections aren't in a similar format to some of the other readme's - for example, the templates section has no tables. To change that kind of thing you'll need someone who reads Japanese.

I've also left the code blocks as indents, I don't see the point in doing extra work to garner the same output.

Aside from that, the markdown looks fine to me.

Iain