i18n: add Russian README translation (closes #3114)

[Aki120900]

Closes #3114

This PR renames i18n/ru/README.md → i18n/ru/README_ru.md and adds a full Russian translation of the project’s README. All content was translated from English to Russian. The top-level README.md has been updated to link to README_ru.md under i18n/ru/. Please review and merge.

[Aki120900]

Hello!
This is my contribution to Issue #3114. I've translated the main README.md file into Russian to help improve accessibility for non-English-speaking users.

I’ve aimed to maintain the tone, clarity, and structure of the original content while ensuring technical accuracy in translation. If there are any changes or suggestions, I’d be more than happy to update the PR.

Thank you very much for the opportunity to contribute — and for the great work on this project!

[Wauplin]

Hey can you move this file under i18n/README_ru.md instead? (no need for nested folder). Also, could you update the README.md and all readmes in i18n/ to reference this new file?

Finally, would you be able to ask someone in the Russian-speaking community if they'd be willing to review the translation itself?

Thank you in advance!