Fix CD drive permission issue with Docker (on ArchLinux)

Fixes #499.

Signed-off-by: JoeLametta <JoeLametta@users.noreply.github.com>

Dockerfile

@@ -1,4 +1,5 @@
 FROM debian:buster
+ARG optical_gid
 
 RUN apt-get update && apt-get install --no-install-recommends -y \
     autoconf \
@@ -51,8 +52,10 @@ RUN curl -o - 'https://ftp.gnu.org/gnu/libcdio/libcdio-paranoia-10.2+2.0.1.tar.b
 
 RUN ldconfig
 
-# add user
+# add user (+ group workaround for ArchLinux)
 RUN useradd -m worker -G cdrom \
+    && if [ -n "${optical_gid}" ]; then groupadd -f -g "${optical_gid}" optical \
+    && usermod -a -G optical worker; fi
     && mkdir -p /output /home/worker/.config/whipper \
     && chown worker: /output /home/worker/.config/whipper
 VOLUME ["/home/worker/.config/whipper", "/output"]

README.md

@@ -82,7 +82,7 @@ Please note that, right now, Docker Hub only builds whipper images for the `amd6
 
 Alternatively, in case you prefer building Docker images locally, just issue the following command (it relies on the [Dockerfile](https://github.com/whipper-team/whipper/blob/develop/Dockerfile) included in whipper's repository):
 
-`docker build -t whipperteam/whipper .`
+`optical_gid=$(getent group optical | cut -d: -f3) docker build --build-arg optical_gid -t whipperteam/whipper .`
 
 It's recommended to create an alias for a convenient usage: