Add build status to README

[skip ci]

Author: matthiasnoback

README.md

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 By Matthias Noback
 
+[![Build Status](https://travis-ci.org/matthiasnoback/symfony-console-form.svg?branch=master)](https://travis-ci.org/matthiasnoback/symfony-console-form)
+
 This package contains a Symfony bundle and some tools which enable you to use Symfony Form types to define and
 interactively process user input from the CLI.