avoid description text overlaps with sidebar.

when I go to http://railscasts-china.com/, I see the description text overlaps with sidebar. See bellow screenshot:

![Snip20130424_1](https://f.cloud.github.com/assets/1198651/419534/4a355400-acd2-11e2-9e83-282b37c15a3d.png)

Seems need to adjust the CSS(margin-right) of .content class