add yay, and "build" user

Dockerfile

@@ -2,6 +2,11 @@ FROM archlinux:latest AS arch
 RUN pacman -Syu base-devel git --noconfirm && sed -i '/E_ROOT/d' /usr/bin/makepkg
 RUN mv /usr/include/bits/stdlib.h /tmp
 RUN perl -n -i -e 'print unless m-bits/stdlib.h-' /usr/include/stdlib.h
+RUN useradd -m -G wheel -s /bin/bash build
+RUN perl -i -pe 's/# (%wheel ALL=\(ALL\) NOPASSWD: ALL)/$1/' /etc/sudoers
+USER build
+RUN cd /tmp && git clone https://aur.archlinux.org/yay.git && cd yay && makepkg -si --noconfirm
+USER root
 COPY entrypoint.sh /entrypoint.sh
 ENTRYPOINT ["/entrypoint.sh"]