Document the China region for users and contributors

docs/update-process.md

@@ -279,6 +279,8 @@ There is no version file at runtime. `omarchy-version` derives the version from
 linked checkout, and `omarchy-version-channel` sniffs the mirrorlist and
 pacman.conf to answer which channel is active.
 
+On a China machine (`/etc/omarchy/region` holds `china`), `omarchy-refresh-pacman` and the installer's `post-install/pacman.sh` run `default/region/china/pacman.sed` over the copied templates, which puts a `.omarchy.cn` twin ahead of every `.omarchy.org` server. The update itself never rewrites these files, so the twins survive every `omarchy update`.
+
 ## Update-related binaries
 
 This inventory is intentionally opinionated. Some commands are useful as stable