Use CI image with unprivileged user

Use CI image with an unprivileged user student, which has no-password sudo
powers, such that the installation snipped from the README.md can be executed
directly.

Dockerfile

@@ -6,9 +6,10 @@ LABEL maintainer "frank@sauerburger.com"
 
 # install python3, setuptools and git
 RUN apt-get update && apt-get install -y  \
-  python3 python3-setuptools git\
+  python3 python3-setuptools git sudo\
   && rm -rf /var/lib/apt/lists/*
 
 # install doxec
-RUN git clone https://srv.sauerburger.com/esel/doxec.git && cd doxec && git checkout b0ce804f && python3 setup.py install
-RUN echo "" | adduser --disabled-password student 
+RUN git clone https://srv.sauerburger.com/esel/doxec.git && cd doxec && git checkout b0ce804f && python3 setup.py install 
+RUN echo "" | adduser --disabled-password student && echo "student ALL=(ALL) NOPASSWD: ALL" >> /etc/sudoers
+USER student

README.md

@@ -22,21 +22,10 @@ analysis and data presentation. To install all the packages on Ubuntu, you
 can run the following command line.
 
 ```bash
-sudo apt-get install python3 python3-pip
-pip3 install --user numpy scipy matplotlib
-```
-<!--
-Doxec in a docker container needs a slightly different command, please keep them
-in-sync.
--->
-<!-- console
-```bash
-$ apt-get update
-$ apt-get -y install python3 python3-pip
-$ su student
+$ sudo apt-get update
+$ sudo apt-get install -y python3 python3-pip
 $ pip3 install --user numpy scipy matplotlib
 ```
--->
 
 # Prerequisites and Structure