Replace the terse install summary with a click-by-click guide that
covers the full setup in both README.md and README.zh-CN.md:
clone+pip, GCP service account, moving the key out of the repo,
creating the sheet with header row, writing config.json, and a
sanity check. Flag the zh-CN tab-name gotcha (工作表1 vs Sheet1)
that causes HTTP 400 Unable to parse range.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
