Add deprecation notice

The new DEC mode 2031 [0] is a much better fit and already has native
support in neovim [1] and tmux [2].
Most terminal emulators either already support it or have it on the
roadmap [3] so with this mode suddenly being support across the whole
stack, it is a much better choice than listening for theme changes with
an extra plugin.

[0] https://contour-terminal.org/vt-extensions/color-palette-update-notifications/
[1] neovim/neovim#31350
[2] tmux/tmux#4353
[3] wezterm/wezterm#6454

Author: vimpostor

README.md

@@ -40,6 +40,11 @@ This also works inside WSL2.
 
 # FAQ
 
+## Is this plugin still needed with latest Vim?
+
+With Neovim [implementing support](https://github.com/neovim/neovim/pull/31350) for [DEC mode 2031](https://contour-terminal.org/vt-extensions/color-palette-update-notifications/) this plugin has become obsolete.
+You can now use the native support for theme changes by reacting to `autocmd OptionSet background`, as long as the entire chain of your terminal emulator, terminal multiplexer and your version of vim support it.
+
 ## How can I add custom callbacks?
 
 You can use the `LumenLight` and `LumenDark` `User` autocommands:

doc/lumen.txt

@@ -23,6 +23,15 @@ All platform implementations are interrupt-based and do not use any resources
 in the background because they avoid polling and use the proper system APIs
 instead.
 
+Note that this plugin has become obsolete with Vim implementing support for
+DEC mode 2031.
+You can now use the native support for theme changes simply by listening to
+`autocmd OptionSet background`, as long as the entire chain of your terminal
+emulator, terminal multiplexer and your version of vim support it.
+For more information read:
+- https://contour-terminal.org/vt-extensions/color-palette-update-notifications/
+- https://github.com/neovim/neovim/pull/31350
+
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 DEPENDENCIES						*lumen-dependencies*