Document .bind(this, element) usecase in lists

See https://groups.google.com/forum/#!topic/reactjs/fjprp2qbPNY

``` javascript
handleClick: function(color, e) {
  this.props.addColor(color);
},
render: function() {
  var items = this.props.colors.forEach(function(color, i) {
    return (
      <li key={i} onClick={this.handleClick.bind(this, color)}>
        {color.name}
      </li>
    );
  }.bind(this));

  return (<ul>{items}</ul>);
}
```
