gh-137760: Update REPL constants documentation

Update documentation for help, quit, and exit constants to reflect
that they can be accessed directly in the interactive interpreter
without parentheses, in addition to the traditional function call syntax.

Author: Antraxmin

Doc/library/constants.rst

@@ -97,15 +97,17 @@ should not be used in programs.
           exit(code=None)
 
    Objects that when printed, print a message like "Use quit() or Ctrl-D
-   (i.e. EOF) to exit", and when called, raise :exc:`SystemExit` with the
+   (i.e. EOF) to exit", and when accessed directly in the interactive 
+   interpreter or called as functions, 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>`.
+   help, or help(object) for help about object.", and when accessed directly
+   in the interactive interpreter, invokes the built-in help system 
+   (see :func:`help`).
 
 .. data:: copyright
           credits