Get historical shares outstanding include date

I am using the following api call

df, err = ek.get_data(
    instruments = ['MSFT.O'],
    fields = ['TR.SharesOutstanding'],
    parameters = {'Frq' : 'D','SDate': '2020-05-01', 'EDate' : '2020-08-25','CH' : 'Fd','RH' : 'date'}
)

I am getting data in the following manner:

   Instrument  Outstanding Shares
0      MSFT.O          7583440247
1      MSFT.O          7583440247
2      MSFT.O          7583440247
3      MSFT.O          7583440247
4      MSFT.O          7583440247
..        ...                 ...
76     MSFT.O          7567652935
77     MSFT.O          7567652935
78     MSFT.O          7567652935
79     MSFT.O          7567652935
80     MSFT.O          7567652935

This is very hard to work with as I don't know the date, it needs a date column as well so I can match the index up. How can I add a date column