Elaborate on running tests in browser

[courajs]

Visting http://localhost:4200 displays the dummy app's "Welcome to Ember" screen. The tests reside at /tests

[sly7-7]

Thank you for the contribution. Thinking a bit more about that, since ember-data is a true ember-cli addon, I wonder if we could just use the basic blueprint generated by ember addon command.

## Installation

* `git clone` this repository
* `npm install`
* `bower install`

## Running Tests

* `npm test` (Runs `ember try:testall` to test your addon against multiple Ember versions)
* `ember test`
* `ember test --server`

## Building

* `ember build`

@bmac @fivetanley Any thoughts ?

[courajs]

That's a good point. There are some advantages to the npm start + /tests method though.
ember test --server does pop up a new chrome instance, which I find a little annoying - it's difficult to cmd+tab to the correct one first try.
Since the filtering/single test rerun support isn't there for the phantom runner, I usually stick to the browser anyway.
Not really sure we want to mention both, since that will be confusing to new contributors. "Why are there two options? Which is better?"

[bmac]

@sly7-7 I'm going to merge this pr as is because it is consistent with how things worked pre ember addon. I'm not opposed to change it to say ember test --server if you or someone else would like to open another pr.