Add .gitlab-ci.yml for Gitlab Pages

1 job for master in 27 seconds (queued for 52 minutes and 47 seconds)
Name Stage Failure
failed
pages Deploy
  File "/usr/local/lib/python3.8/site-packages/jinja2/environment.py", line 832, in handle_exception
reraise(*rewrite_traceback_stack(source=source))
File "/usr/local/lib/python3.8/site-packages/jinja2/_compat.py", line 28, in reraise
raise value.with_traceback(tb)
File "/builds/meige-legi/scientific-computing-m2-efm/ipynb/slides_reveal_wide.tpl", line 2, in top-level template code
{% from 'mathjax.tpl' import mathjax %}
jinja2.exceptions.TemplateNotFound: mathjax.tpl
make: *** [Makefile:36: ipynb/pres07_data_struct.slides.html] Error 1
ERROR: Job failed: exit code 1