build proper dockerized example

docker/Dockerfile.example

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+FROM debian:stretch
+
+RUN apt-get update && apt-get -y install cron python3 sudo procps
+
+# install root cronjob
+COPY docker/var/spool/cron/crontabs /var/spool/cron/crontabs
+RUN chmod 600 /var/spool/cron/crontabs/root
+COPY docker/root/scripts /root/scripts
+
+# install pspy
+COPY bin/pspy64 /usr/bin/pspy
+
+# set up unpriviledged user
+# allows passwordless sudo to start cron as root on startup
+RUN useradd -ms /bin/bash myuser && \
+    adduser myuser sudo && \
+    echo 'myuser ALL=(ALL) NOPASSWD:ALL' >> /etc/sudoers
+USER myuser
+
+# deploy startup script
+COPY docker/entrypoint-example.sh /entrypoint.sh
+RUN sudo chmod +x /entrypoint.sh
+CMD ["/entrypoint.sh"]
+
+