bpo-9842: Add cross-reference to the ellipsis object (GH-4063)

This PR adds a cross-reference to the ellipsis object and the representation of recursive item in containers as indicated in [issue 9842](https://bugs.python.org/issue9842) by @bitdancer.


https://bugs.python.org/issue9842

Doc/glossary.rst

@@ -13,10 +13,14 @@ Glossary
       examples which can be executed interactively in the interpreter.
 
    ``...``
-      The default Python prompt of the interactive shell when entering code for
-      an indented code block, when within a pair of matching left and right
-      delimiters (parentheses, square brackets, curly braces or triple quotes),
-      or after specifying a decorator.
+      Can refer to:
+
+      * The default Python prompt of the interactive shell when entering code for
+        an indented code block, when within a pair of matching left and right
+        delimiters (parentheses, square brackets, curly braces or triple quotes),
+        or after specifying a decorator.
+
+      * The :const:`Ellipsis` built-in constant.
 
    2to3
       A tool that tries to convert Python 2.x code to Python 3.x code by