The English README becomes README.md so the GitHub landing page reads in
English; the Chinese one moves to README.zh-CN.md. Both cross-link at the
top. Drops the source-origin framing from the intro and removes the
Disclaimer section, and points the license badge at MIT.
change-policy and pr-triage hardcoded README.en.md, which would have
dropped README.zh-CN.md out of the docs lane.