installer: don't run zsh at the end

Co-authored-by: Joel Kuzmarski <leoj3n@gmail.com>

tools/install.sh

@@ -219,6 +219,11 @@ main() {
 	EOF
 	printf "$RESET"
 
+	if [ ! -t 0 ]; then
+		echo "${YELLOW}Run zsh to try it out.${RESET}"
+		exit
+	fi
+
 	exec zsh -l
 }