gh-103066: Add links and `help` in site.py constants (#103777)

Co-authored-by: Terry Jan Reedy <tjreedy@udel.edu>
Co-authored-by: Łukasz Langa <lukasz@langa.pl>
Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>
Co-authored-by: Alex Waygood <Alex.Waygood@Gmail.com>

Doc/library/constants.rst

@@ -82,6 +82,8 @@ A small number of constants live in the built-in namespace.  They are:
    :exc:`SyntaxError`), so they can be considered "true" constants.
 
 
+.. _site-consts:
+
 Constants added by the :mod:`site` module
 -----------------------------------------
 
@@ -97,6 +99,13 @@ should not be used in programs.
    (i.e. EOF) to exit", and when called, raise :exc:`SystemExit` with the
    specified exit code.
 
+.. data:: help
+   :noindex:
+
+   Object that when printed, prints the message "Type help() for interactive
+   help, or help(object) for help about object.", and when called,
+   acts as described :func:`elsewhere <help>`.
+
 .. data:: copyright
           credits
 

Doc/library/site.rst

@@ -15,8 +15,9 @@ import can be suppressed using the interpreter's :option:`-S` option.
 
 .. index:: triple: module; search; path
 
-Importing this module will append site-specific paths to the module search path
-and add a few builtins, unless :option:`-S` was used.  In that case, this module
+Importing this module normally appends site-specific paths to the module search path
+and adds :ref:`callables <site-consts>`, including :func:`help` to the built-in
+namespace. However, Python startup option :option:`-S` blocks this and this module
 can be safely imported with no automatic modifications to the module search path
 or additions to the builtins.  To explicitly trigger the usual site-specific
 additions, call the :func:`main` function.