evaluation metrics markdown

[melodiemonod]

Write markdown to summarise the theory behind the evaluation metrics for survival models.

[melodiemonod]

I added a new evaluation_metrics_survival_model.md file in notebooks/

I tried to add it in the sphinx in index.rst with

.. toctree::
    :maxdepth: 2
    :caption: Tutorials:

    notebooks/introduction
    notebooks/momentum
    notebooks/evaluation_metrics_survival_model.md

But the maths mode isn't working

Any idea how to fix this @tcoroller @kruscpe1?