Based on comments from JarnoRFB in
#32 I have updated a few
phrases and rewrote the introduction as it was too unfounded.
Looking at the literature, I found that simulations are also
beneficial due to known outbreak properties, which makes
evaluation possible in the first place in certain situations.

- Flake8 has moved to GitHub: see https://pre-commit.com/hooks.html
- Changed exclude since it is regex and not glob:
pre-commit/pre-commit#1702
- pre-commit assumes immutable ref. Thus, this commit changes
black's ref to a fixed version number. Using an unpinned latest version
is not encouraged.

Major version in sphinx-bibtex is incompatible with this library's
sphinx version. This commit restricts the version number:
executablebooks/jupyter-book#1137 (comment)

The latest release of jinja2 introduces was not compatible with
this library's sphinx version. This commit restricts the version number:
readthedocs/readthedocs.org#9038 (comment)

isort is used in pre-commit hook but does not come with the
requirements-dev.txt. This commit adds it to have it available during
development.

Building the docs with a Jupyter notebook in it requires pandoc. The
README is updated to include an installation instruction. Using
conda is suggested in this stackoverflow question:
https://stackoverflow.com/questions/62398231/building-docs-fails-due-to-missing-pandoc

test_simulations.py was throwing dtype errors since sometimes, n_cases
was int_32 and sometimes int_64. With this commit, data type is casted
to pass the unit test.

Imports were not sorted correctly according to isort which was fixed.

Docstring of simulate was miswritten and missed a "s". This commit
fixes it.