build: adapt Arch Linux packaging

packaging/arch/README.md

@@ -0,0 +1,36 @@
+# Arch package
+
+This PKGBUILD is intended for Arch Linux and AUR-style release packaging. It
+builds from the project release tag, uses Arch system libraries, and disables
+FetchContent so package builds do not download dependencies during CMake
+configure.
+
+Before publishing a release package, replace the temporary `SKIP` checksum in
+`PKGBUILD` with a real checksum, for example by running `updpkgsums` after the
+tag archive is available.
+
+## Build
+
+```fish
+cd packaging/arch
+makepkg -f
+```
+
+## Install
+
+```fish
+cd packaging/arch
+sudo pacman -U qemby-*.pkg.tar.zst
+```
+
+## Run
+
+```fish
+qemby
+```
+
+## Uninstall
+
+```fish
+sudo pacman -R qemby
+```