zh/_index modify for chinese translation correction

[beautytiger]

"Planet Scale" means a global scale which "全球规模" will be better for this description in chinese.
"Designed on the same principles that allows Google to run billions of containers a week" to "基于允许 Google 每周运行数十亿个容器的原则进行设计", it's more natural in chinese.

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[tengqm]

/lgtm
/approve

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