Rewrite idlelib/Icons/README.txt (#123329)

Lib/idlelib/Icons/README.txt

@@ -1,13 +1,36 @@
-The IDLE icons are from https://bugs.python.org/issue1490384
+2006?: Andrew Clover made the 16-, 32-, and 48-bit icons for win23.
+https://www.doxdesk.com/software/py/pyicons.html
+(TJR: Not sure if this originally included 256-bit image.)
 
-Created by Andrew Clover.
+2006: They were copied to CPython as Python application icons.
+https://github.com/python/cpython/issues/43372
+(TJR: I do not remember where put in CPython source tree.)
 
-The original sources are available from Andrew's website:
-https://www.doxdesk.com/software/py/pyicons.html
+2014: They were copied (perhaps a bit revised) to idlelib/Icons.
+https://github.com/python/cpython/issues/64605
+
+2020: Add Clover's 256-bit image.
+https://github.com/python/cpython/issues/82620
+
+The idle.ico file used for Windows was created with ImageMagick:
+  $ convert idle_16.png idle_32.png idle_48.png idle_256.png idle.ico
+** This needs redoing whenever files are changed.
+?? Do Start, Desktop, and Taskbar use idlelib/Icons files?
+
+Issue added Windows Store PC/icons/idlex44.png and .../idlex150.png.
+https://github.com/python/cpython/pull/22817
+** These should also be updated with major changes.
+
+2022: Optimize .png images in CPython repository.
+https://github.com/python/cpython/pull/21348
+idle.ico (and idlex##) were not updated.
+
+The idlexx.gif files are only needed for *nix running tcl/tk 8.5.
+As of 2022, this was known true for 1 'major' Linux distribution.
+(Same would be true for any non-Aqua macOS with 8.5, but must be none.)
 
-Various different formats and sizes are available at this GitHub Pull Request:
-https://github.com/python/cpython/pull/17473
+The other .gifs are used by browsers using idlelib.tree.  At least some
+will not be used when tree is replaced by ttk.Treeview.
 
-The idle.ico file was created with ImageMagick:
 
-    $ convert idle_16.png idle_32.png idle_48.png idle_256.png idle.ico
+Edited 2024 August 25 by TJR.