Add travis build status to README.md

README.md

-# Docker Base Image for Arch Linux
+# Docker Base Image for Arch Linux [![Build Status](https://travis-ci.org/pierres/archlinux-docker.svg?branch=master)](https://travis-ci.org/pierres/archlinux-docker)
 This repository contains all scripts and files needed to crate a Docker base image for the Arch Linux distribution.
 ## Dependencies
 Install the following Arch Linux packages: