bpo-42560: tweaks to intro of Tkinter docs- add macOS, drop ActiveState (GH-27835)

(cherry picked from commit 141c7a4fce8def67baa9d24f542c105b8502893e)

Co-authored-by: Mark Roseman <mark@markroseman.com>
diff --git a/Doc/library/tkinter.rst b/Doc/library/tkinter.rst
index 7483ccd..5d0bf79 100644
--- a/Doc/library/tkinter.rst
+++ b/Doc/library/tkinter.rst
@@ -11,9 +11,8 @@
 --------------
 
 The :mod:`tkinter` package ("Tk interface") is the standard Python interface to
-the Tk GUI toolkit.  Both Tk and :mod:`tkinter` are available on most Unix
-platforms, as well as on Windows systems.  (Tk itself is not part of Python; it
-is maintained at ActiveState.)
+the Tcl/Tk GUI toolkit.  Both Tk and :mod:`tkinter` are available on most Unix
+platforms, including macOS, as well as on Windows systems.
 
 Running ``python -m tkinter`` from the command line should open a window
 demonstrating a simple Tk interface, letting you know that :mod:`tkinter` is