zsh: Set TERM for max compatibility

I'm working with a lot of different systems over ssh
which don't always have the terminfo available (e.g. alacritty,
kitty, foot) and this seems to be the easiest way to solve this.

.zshrc

@@ -44,6 +44,11 @@ source $ZSH/oh-my-zsh.sh
 
 ### User configuration
 
+# Set TERM for with or without TMUX
+# http://www.economyofeffort.com/2014/07/04/zsh/
+export TERM=xterm-256color
+[ -n "$TMUX" ] && export TERM=screen-256color
+
 setopt completealiases
 
 prompt_context(){}