Improved docs for i18n

[NilsJacobsen]

Hey folks,

Doc improvements:

• Added a batch to the top of the page. No it is visible what the current state of the translations is. The batch is dynamically generated by inlang and reflects the current status of the main branch.

[![translation badge](https://inlang.com/badge?url=github.com/AppFlowy-IO/AppFlowy)](https://inlang.com/editor/github.com/AppFlowy-IO/AppFlowy?ref=badge)

• Added the no-code description of how to add a language file to the codebase.

Let me know if we should change something.