[kuxiaowo]

I'm developing a Simplified Chinese localization mod for Kitten Space Agency, and StarMap has been a great help in that work. I'd like to contribute a Simplified Chinese README to help reduce the language barrier for other Chinese-speaking developers.

This PR adds README.zh-CN.md and a language link in the English README. The existing English text remains unchanged.

The translation covers the current upstream README at 74f6505, including the Windows x64 .NET 10 Runtime requirement, the documentation entry point, and the release/RC documentation information. Existing configuration identifiers, example paths, and credits are preserved. The Chinese README links back to the English version.

Validation:

• Confirmed the English README differs from the target branch only by the language link and its blank line.
• Compared all seven sections with the current upstream English README.
• Confirmed the update preserves every pre-existing Chinese paragraph and example, adding only the missing upstream information.
• Checked the reciprocal README links, UTF-8 text, and whitespace. The documentation-source link points to upstream main so it also works while this PR targets the older external-contribution staging branch.

Documentation only; no application code changes.

AI assistance: Codex helped update the translation and run the checks described above.