docs(CHANGES) Note tmux < 3.2a deprecation (via libtmux)

Author: tony

CHANGES

@@ -31,6 +31,12 @@ $ pipx install --suffix=@next 'tmuxp' --pip-args '\--pre' --force
 
 <!-- To maintainers and contributors: Please add notes for the forthcoming version below -->
 
+### Deprecations
+
+- tmux versions below 3.2a are now deprecated (via libtmux). A `FutureWarning`
+  will be emitted on first use. Support for these versions will be removed in
+  a future release. Set `LIBTMUX_SUPPRESS_VERSION_WARNING=1` to suppress.
+
 ### What's new
 
 #### tmux 3.6 support (#989)