Adjust permissions guide layout for small screens

[emiliopavia]

Checklist

• [x] All new and existing tests pass
• [x] I've read the Contribution Guidelines
• [x] I've read Change Limitations

Motivation and Context

This PR fixes #14.

Description

I've adjusted some auto layout constraints in order to better fit in small screens. However I cannot guarantee that this will work for every language, as some labels might be too long to fit with this rigid design.

In the future I'd also suggest to remove the permissions request at the first launch, as it doesn't fit well with the iOS HIG. Instead we should ask for permissions on demand, when the user might need them.

Attached you can see screenshots of the fixed layout.

[emiliopavia]

Honestly I wouldn't spend too much time on such a small edge case. I can try, but instead I would rewrite the entire view controller when really needed.