Correcting documentation to reflect current Testee functionality and syntax

Mainly

* change `--browser` to `--browsers` in examples, and updated help message to reflect the ability to add more than one browser
* updated options for using pagekite. example now uses

``` 
    "tunnel": {
        "type": "pagekite",
        "name": "pagekite-name"
    }
```
Other fixes to documentation, indicating dependency on [phantomJS](http://phantomjs.org) for default testing.