docs: add explanation about freq units in Timedelta.round() (#55149)

Author: Borda

pandas/_libs/tslibs/timedeltas.pyx

@@ -1942,6 +1942,7 @@ class Timedelta(_Timedelta):
         ----------
         freq : str
             Frequency string indicating the rounding resolution.
+            It uses the same units as class contructor :class:`~pandas.Timedelta`.
 
         Returns
         -------
@@ -1969,6 +1970,7 @@ class Timedelta(_Timedelta):
         ----------
         freq : str
             Frequency string indicating the flooring resolution.
+            It uses the same units as class contructor :class:`~pandas.Timedelta`.
 
         Examples
         --------
@@ -1988,6 +1990,7 @@ class Timedelta(_Timedelta):
         ----------
         freq : str
             Frequency string indicating the ceiling resolution.
+            It uses the same units as class contructor :class:`~pandas.Timedelta`.
 
         Examples
         --------