bpo-44693: Update __future__ entry in Doc/glossary.rst (GH-27349) (GH-27357)

Replace sentence with confusing "pseudo-module" with two sentences separating future statements and the __future__ module. Co-authored-by: Terry Jan Reedy <tjreedy@udel.edu> (cherry picked from commit 0363a40) Co-authored-by: Steven Hsu <hsuhaochun@gmail.com> Co-authored-by: Steven Hsu <hsuhaochun@gmail.com>

Author: miss-islington

Doc/glossary.rst

@@ -461,12 +461,13 @@ Glossary
  for best practices on working with annotations.
 
  __future__
- A pseudo-module which programmers can use to enable new language features
- which are not compatible with the current interpreter.
-
- By importing the :mod:`__future__` module and evaluating its variables,
- you can see when a new feature was first added to the language and when it
- becomes the default::
+ A :ref:`future statement <future>`, ``from __future__ import <feature>``,
+ directs the compiler to compile the current module using syntax or
+ semantics that will become standard in a future release of Python.
+ The :mod:`__future__` module documents the possible values of
+ *feature*. By importing this module and evaluating its variables,
+ you can see when a new feature was first added to the language and
+ when it will (or did) become the default::
 
  >>> import __future__
  >>> __future__.division

Misc/NEWS.d/next/Documentation/2021-07-25-23-04-15.bpo-44693.JuCbNq.rst

@@ -0,0 +1,2 @@
+Update the definition of __future__ in the glossary by replacing the confusing
+word "pseudo-module" with a more accurate description.