add tmux install script

install_posix/install_tmux.sh

@@ -0,0 +1,12 @@
+#!/usr/bin/env bash
+echo "configuring tmux.."
+src=`pwd`/../tmux.conf
+dest=${HOME}/.tmux.conf
+if [ -e ${dest} ]; then
+    echo "~/.tmux.conf exists. abort"
+    exit 1
+fi
+
+ln -s ${src} ${dest}
+echo "done."
+