Updated docstrings for missing description

pandas-dev pandas-dev#28792

Author: suparnasnair

pandas/core/arrays/datetimelike.py

@@ -1465,7 +1465,7 @@ def mean(self, skipna=True):
 
         See Also
         --------
-        numpy.ndarray.mean
+        numpy.ndarray.mean : Returns the average of the array elements along given axis.
         Series.mean : Return the mean value in a Series.
 
         Notes