DOC: RT03 Add return value description for Index.where

Author: laymonage

pandas/core/indexes/base.py

@@ -3949,7 +3949,9 @@ def where(self, cond, other=None):
 
         Returns
         -------
-        Index
+        pandas.Index
+            Copy of self with entries replaced from other
+            where the condition is False.
 
         See Also
         --------