Add basic styles to tables in READMEs

Before:

![screen shot 2014-04-02 at 2 26 31 am](https://cloud.githubusercontent.com/assets/7132322/2588292/22f5cf5e-ba38-11e3-9a45-df2a64e41f13.png)

After:

![screen shot 2014-04-02 at 2 25 57 am](https://cloud.githubusercontent.com/assets/7132322/2588290/1343753e-ba38-11e3-9942-1137e24cfb65.png)

Closes #691.