Updating mirr docstring [issue 76]

[RVitalii]

This pull request addresses issue #76 by enhancing the documentation for the mirr function.

I have updated the docstring to provide clearer explanations of the function's purpose, parameters, and usage. Additionally, I incorporated a more detailed MIRR formula, including the reinvestment rate, and provided illustrative examples to guide users in understanding how to use the function effectively.

[Kai-Striega]

Hello @RVitalii,

Thanks for taking the time to make a contribution!

This looks good. There are just a few problems with the style guide. At the moment, the CI is failing because some lines are too long. Here is the output from the CI:

numpy_financial/_financial.py:940:89: E501 Line too long (105 > 88)
numpy_financial/_financial.py:964:89: E501 Line too long (128 > 88)
numpy_financial/_financial.py:967:89: E501 Line too long (99 > 88)

This means that on lines 940,964 and 967 you are exceeding the limit of 88 chars. Would you please shorten those lines and I'll take another look through it?

[RVitalii]

Hello,

I tried to update my forked-main branch from upstream and amend the original commit, but did a lot of mess instead. I didn't know that the iss76 branch is already connected to upstream, and everything I had to do is to update that branch.

Eventually, I managed to push a new commit with the proposed changes:

b04ad78

Please, let me know if I have to correct smth.

Regards,
V.R.

[Kai-Striega]

There's still one check failing. See the Lint check in the CI

Here's the failing output:

ruff 0.1.6
numpy_financial/_financial.py:940:89: E501 Line too long (93 > 88)
Found 1 error.
Error: Process completed with exit code 1.

[RVitalii]

Hello @Kai-Striega,

Updated. Here is the commit number: 4fa06ed

Regards,
V.R.

[Kai-Striega]

@RVitalii thanks for contributing, this looks good now! Are there any last changes you would like to do before I merge it?

[RVitalii]

@Kai-Striega, no I am fine. Thanks for support.

[Kai-Striega]

Merged. Thanks again for taking the time to contribute.