Better doc

Author: xinrong-meng

databricks/koalas/frame.py

@@ -8644,6 +8644,10 @@ def all(self, axis: Union[int, str] = 0) -> "ks.Series":
             * 0 / 'index' : reduce the index, return a Series whose index is the
               original column labels.
 
+        Returns
+        -------
+        Series
+
         Examples
         --------
         Create a dataframe from a dictionary.
@@ -8731,6 +8735,10 @@ def any(self, axis: Union[int, str] = 0) -> "ks.Series":
             * 0 / 'index' : reduce the index, return a Series whose index is the
               original column labels.
 
+        Returns
+        -------
+        Series
+
         Examples
         --------
         Create a dataframe from a dictionary.