Japanese documents are out of date

[doraneko94]

This is about:

• A typo
• Innaccurate/misleading documentation (e.g. technically incorrect advice)
• Undocumented code
• Outdated documentation
• Other

Problem
https://yew.rs/ja/docs/getting-started/build-a-sample-app
The Japanese-language documentation is out of date.
The other pages also need updating, but for the time being the Getting started page should be up-to-date for new users.

Details about the solution you'd like (Optional)
As long as you tell me where to find the files that need to be updated, I will translate the latest content into Japanese.
(I have not yet discovered where the original Japanese documentation is located in this repository.)

Questionaire (Optional)

• I'd like to write this documentation
• I'd like to write this documentation but I'm not sure what's needed
• I don't have time to add this right now, but maybe later

[msfjarvis]

https://github.com/yewstack/yew/tree/master/website%2Fi18n%2Fja%2Fdocusaurus-plugin-content-docs

This should be it.