Merge pull request numpy#27168 from guan404ming/mean-td64-doc

DOC: add td64 example in `np.mean`

Author: jorenham

numpy/_core/fromnumeric.py

@@ -3884,6 +3884,12 @@ def mean(a, axis=None, dtype=None, out=None, keepdims=np._NoValue, *,
     >>> np.mean(a, dtype=np.float64)
     0.55000000074505806 # may vary
 
+    Computing the mean in timedelta64 is available:
+    
+    >>> b = np.array([1, 3], dtype="timedelta64[D]")
+    >>> np.mean(b)
+    np.timedelta64(2,'D')
+
     Specifying a where argument:
 
     >>> a = np.array([[5, 9, 13], [14, 10, 12], [11, 15, 19]])