Add notebooks + better index page

1 job for master in 24 seconds (queued for 2 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.tpl", line 2, in top-level template code
{% from 'mathjax.tpl' import mathjax %}
jinja2.exceptions.TemplateNotFound: mathjax.tpl
make: *** [Makefile:43: ipynb/080_oop_encapsulation.slides.html] Error 1
ERROR: Job failed: exit code 1