doc: Add links to translated README versions

[dowithless]

Added language selection links to the README for easier access to translated versions: German, Spanish, French, Japanese, Korean, Portuguese, Russian, and Chinese.

The updated links can be previewed in my forked repository: https://github.com/dowithless/stagehand/tree/patch-3

why

what changed

test plan

[dowithless]

For Chinese users, we’ve also added a Chinese version of the docs! Check it out here: https://stagehand.readme-i18n.com/zh