ember-cli 0.1.5 updates

No major changes for this update, just a simple editor option change.
Feature detect .addBowerPackagesToProject()

Since .addBowerPackagesToProject() was added so recently, I’ve
introduce backwards compatibility with the previous way of doing so,
individually by chaining .addBowerPackageToProject(). Now this addon
should work going back to ember-cli 0.0.41
Include ember install:addon to documentation

With ember-cli 0.1.5, it’s possible to invoke `ember install:addon
ember-cli-bootswatch` which will both npm install the addon along with
running the addon blueprint to install bower deps. Also explicitly
stated the install steps depending on project ember-cli version.