Add component.json to install as Bower package

This will allow "add-to-homescreen" to be easily installed in any project via the [Bower](http://twitter.github.com/bower/) package manager with the command:

```bash
$ bower install add-to-homescreen
```

After merging this you will need to register your repo as a Bower package with:

```bash
$  bower register add-to-homescreen git://github.com/cubiq/add-to-homescreen
```

(See "Authoring packages" on the [Bower](http://twitter.github.com/bower/) site)

I think you should also tag your stable commit with a version number:

```bash
$ git tag -a 2.0.6 -m "Release 2.0.6"
```

You can see all the Bower packages already out there: http://sindresorhus.com/bower-components/

Thanks!
Nicolas