DOC: MIRR documentation is lacking

[Kai-Striega]

Issue with current documentation:

The documentation for MIRR is very limited (see below screenshot)

Idea or request for content:

The documentation for MIRR should explain what it is, how to use it and when to use it. In addition, in should supply some examples of how it should be used

[RVitalii]

Hello,

Is it enough to change the description inside the docstring of the MIRR function?

Regards,
VR

[Kai-Striega]

Yes, changing the description inside the doc string should be good, saying that I quite like what you have done with your PR

[Kai-Striega]

Closed in #86. So closing this issue