Dockerfile: manually symlink os-release

Dockerfile

@@ -5,6 +5,9 @@ ADD archlinux.tar.xz /
 RUN ldconfig && update-ca-trust && locale-gen 
 RUN sh -c 'ls usr/lib/sysusers.d/*.conf | /usr/share/libalpm/scripts/systemd-hook sysusers '
 
+# update /etc/os-release
+RUN ln -s /usr/lib/os-release /etc/os-release
+
 # initialize the archilnux keyring, but discard any private key that may be shipped.
 RUN pacman-key --init && pacman-key --populate archlinux
 RUN rm -rf etc/pacman.d/gnupg/{openpgp-revocs.d/,private-keys-v1.d/,pugring.gpg~,gnupg.S.}*