Merge pull request #62 from grafana/readme-image-tweak

Centers badges in the readme

README.md

 <p align="center"><img src="docs/logo_and_name.png" width="600" alt="Loki Logo"></p>
 
-[![CircleCI](https://circleci.com/gh/grafana/loki/tree/master.svg?style=svg&circle-token=618193e5787b2951c1ea3352ad5f254f4f52313d)](https://circleci.com/gh/grafana/loki/tree/master) [![Slack](https://img.shields.io/badge/join%20slack-%23loki-brightgreen.svg)](http://slack.raintank.io/)
+<p align="center">
+<a href="https://circleci.com/gh/grafana/loki/tree/master"><img src="https://circleci.com/gh/grafana/loki.svg?style=svg&circle-token=618193e5787b2951c1ea3352ad5f254f4f52313d" alt="CircleCI" /></a>
+<a href="http://slack.raintank.io/"><img src="https://img.shields.io/badge/join%20slack-%23loki-brightgreen.svg" alt="Slack" /></a>
+</p>
 
 # Grafana Loki: like Prometheus, but for logs.