fix: automate arch packaging

using docker just like debian. This makes the scripts easier to
reproduce.

scripts/package-sci-arch.sh

@@ -0,0 +1,21 @@
+#!/bin/bash
+archbuilder_image=$(docker images | grep archbuilder)
+set -e
+if [ -z $archbuilder_image ]; then
+    echo "building archbuilder image..."
+    docker build -t archbuilder -f arch-builder.dockerfile .
+fi
+
+echo "building source dist..."
+make dist
+SRC_SHA256=$(sha256sum sci-1.0.0.tar.gz | awk '{ print $1 }')
+echo $SRC_SHA256
+sed "s/SRC_SHA256/$SRC_SHA256/g" < PKGBUILD.in > PKGBUILD
+
+echo "building arch package in archbuilder docker image..."
+docker run --rm -it -v .:/src archbuilder sh -c '\
+    cd && \
+    cp /src/sci-1.0.0.tar.gz /src/PKGBUILD . && \
+    makepkg && \
+    cp *.zst /src
+'