DOC: point out that only period frequencies are valid for to_period (#53477)

point out that only period frequencies are valid for  to_period

Author: natmokval

pandas/core/arrays/datetimes.py

@@ -1139,9 +1139,9 @@ def normalize(self) -> Self:
 
     def to_period(self, freq=None) -> PeriodArray:
         """
-        Cast to PeriodArray/Index at a particular frequency.
+        Cast to PeriodArray/PeriodIndex at a particular frequency.
 
-        Converts DatetimeArray/Index to PeriodArray/Index.
+        Converts DatetimeArray/Index to PeriodArray/PeriodIndex.
 
         Parameters
         ----------