Backport PR #39064: Added docs for the change of behavior of isin (#39230)

Co-authored-by: Omar Afifi <omarafifi@windowslive.com>

Author: meeseeksmachine

pandas/core/series.py

@@ -4622,6 +4622,15 @@ def isin(self, values) -> "Series":
         4     True
         5    False
         Name: animal, dtype: bool
+
+        Strings and integers are distinct and are therefore not comparable:
+
+        >>> pd.Series([1]).isin(['1'])
+        0    False
+        dtype: bool
+        >>> pd.Series([1.1]).isin(['1.1'])
+        0    False
+        dtype: bool
         """
         result = algorithms.isin(self._values, values)
         return self._constructor(result, index=self.index).__finalize__(