[DOC] Optional parameters and lists of posible inputs for parameters

[mberz]

We're need to add a description of how to specify lists of possible inputs for function parameters ( such as only specific strings, etc.)

https://numpydoc.readthedocs.io/en/latest/format.html#parameters

[hoyer-a]

Here are some examples how numpy handles those cases in their own documentation:

strings:
https://numpy.org/doc/stable/reference/generated/numpy.fft.fft.html#numpy.fft.fft#
https://numpy.org/doc/stable/reference/generated/numpy.linalg.eigh.html

mixed input types:
https://numpy.org/doc/stable/reference/generated/numpy.linalg.norm.html
https://numpy.org/doc/stable/reference/generated/numpy.genfromtxt.html (e.g. case_sensitive)