DOC: fix andas.Series.str.fullmatch RT03

Author: KatsiarynaDzibrova

pandas/core/strings/accessor.py

@@ -1411,6 +1411,9 @@ def fullmatch(self, pat, case: bool = True, flags: int = 0, na=None):
         Returns
         -------
         Series/Index/array of boolean values
+            The function returns a Series, Index, or array of boolean values,
+            where True indicates that the entire string matches the regular
+            expression pattern and False indicates that it does not.
 
         See Also
         --------