docs(README) Python minimum 3.9 -> 3.10

See also:
- https://devguide.python.org/versions/#:~:text=Release%20manager-,3.9,-PEP%20596
- https://peps.python.org/pep-0596/

Author: tony

README.md

@@ -265,7 +265,7 @@ See donation options at <https://tony.sh/support.html>.
 # Project details
 
 - tmux support: 1.8+
-- python support: >= 3.9, pypy, pypy3
+- python support: >= 3.10, pypy, pypy3
 - Source: <https://github.com/tmux-python/libtmux>
 - Docs: <https://libtmux.git-pull.com>
 - API: <https://libtmux.git-pull.com/api.html>