doc: change 'implementation' to 'feature' in snapshot guide

[yahonda]

The term 'implementation' was likely a direct translation from Chinese '实现' and sounds unnatural in English. This also prevents unnatural translations in other languages, such as '実装' in Japanese.

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[gemini-code-assist]

Code Review

This pull request updates the BR snapshot guide to refer to snapshot backup as a "feature" rather than an "implementation". The reviewer suggested rephrasing the sentence to use the second person ("you") and active voice ("completes" instead of "is completed") to align with the style guide.