Fix markdown syntax in README.md

* before
![2013-12-06 23 59 24](https://f.cloud.github.com/assets/290782/1693001/0c42008c-5e87-11e3-89e9-c09c8a39e14a.png)

* after
![2013-12-06 23 59 30](https://f.cloud.github.com/assets/290782/1693004/0ec8a23e-5e87-11e3-8265-9417fe047156.png)