Document other performance implication for __slots__ (GH-11974)



diff --git a/Doc/reference/datamodel.rst b/Doc/reference/datamodel.rst
index 9961aee..9422ae6 100644
--- a/Doc/reference/datamodel.rst
+++ b/Doc/reference/datamodel.rst
@@ -1727,6 +1727,7 @@
 (unless explicitly declared in *__slots__* or available in a parent.)
 
 The space saved over using *__dict__* can be significant.
+Attribute lookup speed can be significantly improved as well.
 
 .. data:: object.__slots__