Show title and description from schema

See https://github.com/atom/atom/pull/3613 for context.

Render the title and description when available.

![screen shot 2014-09-30 at 10 12 54 am](https://cloud.githubusercontent.com/assets/671378/4462687/15151f36-48c5-11e4-8072-098a853ca4e4.png)
![screen shot 2014-09-30 at 10 12 48 am](https://cloud.githubusercontent.com/assets/671378/4462681/0bb3d19e-48c5-11e4-8dbb-e3ef6a4cb862.png)

/cc @benogle