Add keychain sharing entitlement to sign with dev certificate on macOS

[mdmathias]

Fixes #192

Related to discussion in #191.

[petea]

Any insight into why this is the behavior for the development cert case on macOS?

You didn't need to add keychain sharing with our internal development cert, correct?

[mdmathias]

The issue is that running the sample app on macOS is, I guess, similar to deploying to a real device. That means there is a discrepancy between what the iOS and macOS sample apps need in order to work. iOS will not need a provisioning profile if deploying on the simulator. macOS will because you are deploying to a real device. I think this difference is a little confusing.

In any case, macOS users have two options:

1. Manually manage signing and provide a provisioning profile.
2. Add the keychain-access-groups entitlement to the mac target.

I think we should suggest in that order. I'm going to update our README to provide some guidance on this.

[dav3yblaz3]

this looks like this could work thank you