Create Japanese documentation page.

[nodematerial]

I begun translating the documentation into Japanese.

In detail, I worked on following tasks in each commit.

• Copied /docs of https://github.com/test-prof/test-prof to this repository.
• translated README.md into Japanese
• translated getting_started page and sidebar

I will translate the remaining pages in order.

[palkan]

Thanks!

Added you as a collaborator, so you can contribute directly.