Implement docstrings for all functions

[Ludee]

We are using NumPy Style Docstrings.
See: https://sphinxcontrib-napoleon.readthedocs.io/en/latest/example_numpy.html#example-numpy

example:

def example_method(self, param1, param2):
        """Class methods are similar to regular functions.

        Note
        ----
        Do not include the `self` parameter in the ``Parameters`` section.

        Parameters
        ----------
        param1
            The first parameter.
        param2
            The second parameter.

        Returns
        -------
        bool
            True if successful, False otherwise.

        """
        return True