Add support for simctl pair

[ZevEisenberg]

$ 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:

`xcrun simctl pair #{watch_device.udid} #{phone_device.udid}`

But it would be nice not to have to.