Add support for `simctl pair`

```sh
$ xcrun simctl pair help
Create a new watch and phone pair.
Usage: simctl pair <watch device> <phone device>
```

I didn't see reference to the word "pair" in this repo, so it looks like it's not supported. I can easily work around it in a ruby script using:

```rb
`xcrun simctl pair #{watch_device.udid} #{phone_device.udid}`
```

But it would be nice not to have to.