feat: add entry point to docker and use slim image

building/docker/linux.dockerfile

@@ -1,5 +1,15 @@
-#### Creating the container
+# A tiny debian with node binary installed
-FROM node:12-buster
+FROM node:12-slim
+
+# add setup_cpp.js
 ADD "./dist/" "/"
 WORKDIR "/"
+
+# install unzip and xz-utils for the slim image (a standard debian already has these)
+RUN apt-get update -qq
+RUN apt-get install -y --no-install-recommends unzip
+
+# run installation
 RUN node ./setup_cpp.js --compiler llvm --cmake true --ninja true --ccache true --conan true
+
+ENTRYPOINT [ "/bin/sh" ]