fix formatting of brackets in 'bond' section of README.md

#### Before:
![screen shot 2013-12-23 at 11 04 08 am](https://f.cloud.github.com/assets/209264/1801974/64cc2f3c-6bf4-11e3-870f-273a42f225d0.png)

#### After:
![screen shot 2013-12-23 at 11 04 28 am](https://f.cloud.github.com/assets/209264/1801982/a541c202-6bf4-11e3-9d71-700b5079580b.png)