Make the Certify screen a little more self-explanatory

Hm, Studio’s indentation on XML seems to disagree with what’s there in some cases.

See bug https://github.com/open-keychain/open-keychain/issues/971
Not sure about this one.
I liked the notion of "synchronize" because this is the important take away for average users: That their certifications are available everywhere after uploading them to the cloud.
so what about: "Synchronize with the cloud"?