README.ja.md: Japanese documentation is quite old.

[daikimatsura]

Describe the issue

Issue Title

Outdated Japanese Documentation in README.ja.md

Description

The Japanese documentation (README.ja.md) is significantly outdated compared to the current version of the project. This creates confusion for Japanese-speaking users and contributors.

Details

• File affected: README.ja.md

Impact

Japanese-speaking users are unable to properly understand or use the project based on the current documentation.

Proposed Solution

I would be willing to help update the Japanese documentation to match the current English version if that would be helpful.

Links

https://github.com/awslabs/sbt-aws/blob/1a7cdeb1fc24ca2198ccb23bcc543d14dd93c0df/docs/public/README.ja.md