help/zh_CN/: Add help translation (Simplified Chinese) from Damned Lies

Hi, GNOME Simplified Chinese (zh_CN) translation coordinator here.

As I am looking into committing translation from https://l10n.gnome.org/vertimus/loupe/main/help/zh_CN/ into upstream Loupe repository. The l10n.gnome.org website states that the creation of translation file must be manually processed in the git repo first. Please merge this initial translation manually. After merged, I will handle it on l10n.gnome.org directly.

Please let me know if you have any questions. Thanks!