Comments added

Dockerfile

 FROM centos:7
 MAINTAINER stefano.bagnasco@to.infn.it
 
+# Install needed python libraries
 RUN yum install -y numpy python-matplotlib &&\
     yum clean all
 
+# Add the script file
 COPY mandelbrot.py /usr/lib/mandelbrot.py
 RUN chmod a+x /usr/lib/mandelbrot.py
 
+# Define entrypoint and default values for args
 ENTRYPOINT ["/usr/lib/mandelbrot.py"]
 CMD ["50", "50.", "601", "401"]
\ No newline at end of file