Merge pull request #224 from dlorenc/readme

Two readme tweaks:

README.md

-## What is Minikube
+# Minikube
+
+[![Build Status](https://travis-ci.org/kubernetes/minikube.svg?branch=master)](https://travis-ci.org/kubernetes/minikube)
+
+## What is Minikube?
 
 Minikube is a tool that makes it easy to run Kubernetes locally. Minikube runs a single-node Kubernetes cluster inside a VM on your laptop for users looking to try out Kubernetes or develop with it day-to-day.