[Documentation] Document usage of <select>

@leifdenby came to IRC as he couldn't get `<select><options>...</select>` working. It wasn't clear to me that we should use `value={...}` on the `<select>` itself rather than `selected={...}` on `<option>`s. We need to make the doc clearer here.

Here's a JSFiddle that gives 3 examples: Controlled, Controller with LinkState and Uncontrolled `<select>`

http://jsfiddle.net/5734W/
