Added Documentation to specify that DataFrame.last() needs the index to be sorted to deliver the expected results (pandas-dev#38536)

* Update generic.py

Added Documentation mentioning that DataFrame.last() needs the index to be sorted to deliver the expected results

* Update generic.py

Fixed PEP8 Issues

* Update generic.py

Fixed PEP 8  Issues

* Update generic.py

As per recommendation changed the description for DataFrame.last() making it more concise

* Update generic.py

Removed trailing whitespace to fix PEP 8 Issues

Author: aflah02

pandas/core/generic.py

@@ -8439,8 +8439,8 @@ def last(self: FrameOrSeries, offset) -> FrameOrSeries:
         """
         Select final periods of time series data based on a date offset.
 
-        When having a DataFrame with dates as index, this function can
-        select the last few rows based on a date offset.
+        For a DataFrame with a sorted DatetimeIndex, this function
+        selects the last few rows based on a date offset.
 
         Parameters
         ----------