np.pmt documentation is misleading on calculating monthly rate

Documentation

To calculate the monthly rate, you should calculate as (1 + annual_rate) ** (1/12) - 1 rather than simply divide it by 12.

    Examples
    --------
    >>> import numpy_financial as npf

    What is the monthly payment needed to pay off a $200,000 loan in 15
    years at an annual interest rate of 7.5%?

    >>> npf.pmt(0.075/12, 12*15, 200000)
    -1854.0247200054619

    In order to pay-off (i.e., have a future-value of 0) the $200,000 obtained
    today, a monthly payment of $1,854.02 would be required.  Note that this
    example illustrates usage of `fv` having a default value of 0.

Should be rephrased to

    Examples
    --------
    >>> import numpy_financial as npf

    What is the monthly payment needed to pay off a $200,000 loan in 15
    years at an annual interest rate of 7.5%?

    >>> npf.pmt(1.075**(1/12) - 1, 12*15, 200000)
    -1826.1657857130267

    In order to pay-off (i.e., have a future-value of 0) the $200,000 obtained
    today, a monthly payment of $1,826.17 would be required.  Note that this
    example illustrates usage of `fv` having a default value of 0.

https://github.com/numpy/numpy-financial/blob/master/numpy_financial/_financial.py#L220-L232

Read the npf.pmt documentation example in numpy_financial/_financial.py around lines 220-232. Update the monthly-rate calculation, payment result, and explanatory wording to match the corrected example; done means the docstring no longer recommends dividing the annual rate by 12.