Translated of README.markdown and CONTRIBUTING.markdown into Japanese.

I translated README.markdown and CONTRIBUTING.markdown into Japanese.
But I didn't know the following...

1. How to create a NEW document.
  - The rule of the filename.
    - I was named " *.ja.markdown ".
  - Where placed NEW document.
    - Same as " *.markdown " at the project root.
2. The rule for translating text.
  - I replaced text from English to Japanese after I translated original text.

I've read CONTRIBUTING.markdown and "Updating Documentation" of http://jekyllrb.com/docs/contributing/ .
I will follow the rules.