Finishes Dockerfile for running

Dockerfile

@@ -1,4 +1,4 @@
-FROM ubuntu:19.04
+FROM debian:10-slim
 
 WORKDIR /build
 
@@ -7,20 +7,37 @@ COPY . .
 # Add the key for the crystal debian repo
 ADD https://keybase.io/crystal/pgp_keys.asc /tmp/crystal.gpg
 
-# Install gnupg for the apt-key operation and openssl for our TLS stuff
-RUN apt-get update && \
-	apt-get install  --yes --no-install-recommends gnupg=2.2.12-1ubuntu3 libssl-dev=1.1.1b-1ubuntu2.4 && \
+# See https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=863199 for why mkdir is needed
+RUN mkdir -p /usr/share/man/man1 && \
+	apt-get update && \
+	apt-get install  --yes --no-install-recommends \
+	# Install gnupg for the apt-key operation
+	gnupg=2.2.12-1+deb10u1 \
+	# libssl for faster TLS in Crystal
+	libssl-dev=1.1.1d-0+deb10u2 \
+	# pdftk as a dependency for muse-dl
+	pdftk=2.02-5 \
+	# ca-certificates for talking to crystal-lang.org
+	ca-certificates=20190110 \
+	# git to let shards install happen
+	git=1:2.20.1-2+deb10u1 \
+	# build --release
+	zlib1g-dev=1:1.2.11.dfsg-1 && \
 	# See https://crystal-lang.org/install/
 	apt-key add /tmp/crystal.gpg && \
 	echo "deb https://dist.crystal-lang.org/apt crystal main" > /etc/apt/sources.list.d/crystal.list && \
 	apt-get update && \
-	apt-get install --no-install-recommends --yes crystal=0.33.0-1 pdftk=2.02-5 && \
+	apt-get install --no-install-recommends --yes crystal=0.33.0-1 && \
 	# Cleanup
 	apt-get clean && \
 	rm -rf /var/lib/apt/lists/*
 
-RUN shards install && shards build --release
+RUN shards install && shards build --release && \
+	ln /build/bin/muse-dl /usr/bin/muse-dl
 
-VOLUME /output
+RUN apt-get --yes remove git gnupg
 
-ENTRYPOINT ["/build/bin/muse-dl"]
+WORKDIR /data
+VOLUME /data
+
+ENTRYPOINT ["/usr/bin/muse-dl"]