docs(README): update minimum tmux version to 3.2+

why: Support for tmux < 3.2 has been dropped.
what:
- Update tmux support from 1.8+ to 3.2+

Author: tony

README.md

@@ -264,7 +264,7 @@ See donation options at <https://tony.sh/support.html>.
 
 # Project details
 
-- tmux support: 1.8+
+- tmux support: 3.2+
 - python support: >= 3.10, pypy, pypy3
 - Source: <https://github.com/tmux-python/libtmux>
 - Docs: <https://libtmux.git-pull.com>