tmux: Set renumber-windows

[renumber-windows][1]:

> If on, when a window is closed in a session, automatically renumber
> the other windows in numerical order. This respects the base-index
> option if it has been set. If off, do not renumber the windows.

[1]: tmux(1)

.config/tmux/tmux.conf

@@ -37,6 +37,9 @@ bind-key -T prefix R source-file "$XDG_CONFIG_HOME/tmux/tmux.conf" \; display-me
 # Fullscreen pane (toggle)
 bind-key -T prefix F resize-pane -Z
 
+# Automatically renumber windows when closing one
+set -g renumber-windows on
+
 # Vim-bindings
 
 # Enter copy-mode with Escape