Translation of  ja/usage

I started translation of files in ja/usage directory.
Translation of ja/usage/faq.md in PR #1 is also included.

- [x] ja/usage/index.md
- [x] ja/usage/configuration.md
- [x] ja/usage/settings.md
- [x] ja/usage/managing.md
- [x] ja/usage/writing.md
- [x] ja/usage/faq.md